[SPARK-12962] [SQL] [PySpark] PySpark support covar_samp and covar_pop
[SPARK-12962] [SQL] [PySpark] PySpark support covar_samp and covar_pop

PySpark support ```covar_samp``` and ```covar_pop```.

cc rxin davies marmbrus

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #10876 from yanboliang/spark-12962.

janewangfb/spark,someorz/spark,someorz/spark,shubhamchopra/spark,sahilTakiar/spark,apache/spark,huang1900/spark,shubhamchopra/spark,shuangshuangwang/spark,LantaoJin/spark,metamx/spark,narahari92/spark,szhem/spark,mzl9039/spark,patrick-nicholson/spark,xuanyuanking/spark,poffuomo/spark,Panos-Bletsos/spark-cost-model-optimizer,hvanhovell/spark,huang1900/spark,kevinyu98/spark,andrewor14/spark,techaddict/spark,wzhfy/spark,saltstar/spark,liutang123/spark,jkbradley/spark,guoxiaolongzte/spark,big-pegasus/spark,shuangshuangwang/spark,bOOm-X/spark,taroplus/spark,ueshin/apache-spark,mike0sv/spark,icexelloss/spark,ioana-delaney/spark,joseph-torres/spark,poffuomo/spark,saturday-shi/spark,dongjoon-hyun/spark,debugger87/spark,caneGuy/spark,adrian-ionescu/apache-spark,jlopezmalla/spark,gioenn/xSpark,someorz/spark,apache-spark-on-k8s/spark,sachintyagi22/spark,rikima/spark,byakuinss/spark,apache-spark-on-k8s/spark,shubhamchopra/spark,vinodkc/spark,wangyum/spark,patrick-nicholson/spark,WindCanDie/spark,panfengfeng/spark,ericvandenbergfb/spark,techaddict/spark,cloud-fan/spark,ioana-delaney/spark,aokolnychyi/spark,actuaryzhang/spark,zhouyejoe/spark,apache/spark,esi-mineset/spark,dongjoon-hyun/spark,chuckchen/spark,UndeadBaneGitHub/spark,gioenn/xSpark,rezasafi/spark,apache-spark-on-k8s/spark,actuaryzhang/spark,ajaysaini725/spark,zuotingbing/spark,nilsgrabbert/spark,kevinyu98/spark,skonto/spark,szhem/spark,map222/spark,Aegeaner/spark,nilsgrabbert/spark,ericvandenbergfb/spark,aokolnychyi/spark,LantaoJin/spark,BryanCutler/spark,Panos-Bletsos/spark-cost-model-optimizer,Panos-Bletsos/spark-cost-model-optimizer,holdenk/spark,zuotingbing/spark,ibm-research-ireland/sparkoscope,liutang123/spark,jrshust/spark,map222/spark,apache/spark,liyichao/spark,caneGuy/spark,JerryLead/spark,hvanhovell/spark,icexelloss/spark,JerryLead/spark,Panos-Bletsos/spark-cost-model-optimizer,SHASHANKB/spark,shaneknapp/spark,wangmiao1981/spark,aray/spark,patrick-nicholson/spark,wangmiao1981/spark,aokolnychyi/spark,nlalevee/spark,bdrillard/spark,jlopezmalla/spark,pgandhi999/spark,ahnqirage/spark,kimoonkim/spark,andrewor14/spark,BryanCutler/spark,mahak/spark,rednaxelafx/apache-spark,ConeyLiu/spark,WindCanDie/spark,chuckchen/spark,ioana-delaney/spark,kevinyu98/spark,saltstar/spark,ptkool/spark,mdespriee/spark,sahilTakiar/spark,jianran/spark,alunarbeach/spark,caneGuy/spark,rezasafi/spark,cin/spark,big-pegasus/spark,zuotingbing/spark,janewangfb/spark,spark-test/spark,witgo/spark,BryanCutler/spark,zero323/spark,actuaryzhang/spark,patrick-nicholson/spark,publicRoman/spark,ron8hu/spark,WeichenXu123/spark,JoshRosen/spark,jianran/spark,kimoonkim/spark,michalsenkyr/spark,taroplus/spark,UndeadBaneGitHub/spark,kimoonkim/spark,debugger87/spark,saltstar/spark,kiszk/spark,nchammas/spark,vinodkc/spark,aosagie/spark,ron8hu/spark,liyichao/spark,janewangfb/spark,esi-mineset/spark,zhouyejoe/spark,bdrillard/spark,Aegeaner/spark,michalsenkyr/spark,kevinyu98/spark,pgandhi999/spark,zzcclp/spark,kissmetrics/spark,kevinyu98/spark,facaiy/spark,andrewor14/spark,taroplus/spark,Aegeaner/spark,wangmiao1981/spark,joseph-torres/spark,UndeadBaneGitHub/spark,poffuomo/spark,jkbradley/spark,zzcclp/spark,zuotingbing/spark,1haodian/spark,vinodkc/spark,dbtsai/spark,shubhamchopra/spark,maropu/spark,aokolnychyi/spark,Panos-Bletsos/spark-cost-model-optimizer,liyichao/spark,ptkool/spark,wangyum/spark,eyalfa/spark,rikima/spark,zhouyejoe/spark,rikima/spark,apache-spark-on-k8s/spark,JerryLead/spark,aray/spark,stanzhai/spark,map222/spark,sachintyagi22/spark,icexelloss/spark,goldmedal/spark,debugger87/spark,dongjoon-hyun/spark,ConeyLiu/spark,alunarbeach/spark,metamx/spark,byakuinss/spark,rednaxelafx/apache-spark,srowen/spark,adrian-ionescu/apache-spark,MLnick/spark,setjet/spark,hhbyyh/spark,guoxiaolongzte/spark,lvdongr/spark,pgandhi999/spark,adrian-ionescu/apache-spark,milliman/spark,sachintyagi22/spark,shuangshuangwang/spark,JoshRosen/spark,saltstar/spark,someorz/spark,map222/spark,eyalfa/spark,brad-kaiser/spark,akopich/spark,nchammas/spark,gioenn/xSpark,debugger87/spark,yanboliang/spark,aosagie/spark,srowen/spark,sureshthalamati/spark,mahak/spark,sachintyagi22/spark,nilsgrabbert/spark,ptkool/spark,byakuinss/spark,SnappyDataInc/spark,xuanyuanking/spark,pgandhi999/spark,LantaoJin/spark,darionyaphet/spark,mike0sv/spark,ericvandenbergfb/spark,setjet/spark,eyalfa/spark,ericvandenbergfb/spark,bOOm-X/spark,big-pegasus/spark,witgo/spark,yanboliang/spark,witgo/spark,bravo-zhang/spark,wzhfy/spark,akopich/spark,Panos-Bletsos/spark-cost-model-optimizer,SnappyDataInc/spark,kevinyu98/spark,shuangshuangwang/spark,jkbradley/spark,chuckchen/spark,dbtsai/spark,loneknightpy/spark,tejasapatil/spark,aosagie/spark,maropu/spark,rekhajoshm/spark,ibm-research-ireland/sparkoscope,metamx/spark,jlopezmalla/spark,kissmetrics/spark,kevinyu98/spark,SHASHANKB/spark,kimoonkim/spark,UndeadBaneGitHub/spark,ddna1021/spark,byakuinss/spark,publicRoman/spark,liutang123/spark,lxsmnv/spark,publicRoman/spark,markhamstra/spark,joseph-torres/spark,byakuinss/spark,aosagie/spark,liyichao/spark,skonto/spark,srowen/spark,kissmetrics/spark,sureshthalamati/spark,big-pegasus/spark,rednaxelafx/apache-spark,mzl9039/spark,kimoonkim/spark,loneknightpy/spark,cloud-fan/spark,HyukjinKwon/spark,wzhfy/spark,guoxiaolongzte/spark,JoshRosen/spark,1haodian/spark,mike0sv/spark,eyalfa/spark,wangmiao1981/spark,hvanhovell/spark,panfengfeng/spark,jianran/spark,byakuinss/spark,wangyum/spark,witgo/spark,ibm-research-ireland/sparkoscope,alunarbeach/spark,nlalevee/spark,rezasafi/spark,gengliangwang/spark,techaddict/spark,milliman/spark,skonto/spark,stanzhai/spark,gengliangwang/spark,saturday-shi/spark,loneknightpy/spark,ajaysaini725/spark,lvdongr/spark,huang1900/spark,publicRoman/spark,zero323/spark,SnappyDataInc/spark,adrian-ionescu/apache-spark,mzl9039/spark,pgandhi999/spark,holdenk/spark,ron8hu/spark,xuanyuanking/spark,nchammas/spark,ron8hu/spark,zero323/spark,tengpeng/spark,apache-spark-on-k8s/spark,taroplus/spark,witgo/spark,ddna1021/spark,alunarbeach/spark,zero323/spark,zero323/spark,Panos-Bletsos/spark-cost-model-optimizer,brad-kaiser/spark,tejasapatil/spark,maropu/spark,jianran/spark,rekhajoshm/spark,kiszk/spark,Aegeaner/spark,szhem/spark,loneknightpy/spark,liyichao/spark,mahak/spark,rekhajoshm/spark,dbtsai/spark,jiangxb1987/spark,ueshin/apache-spark,xuanyuanking/spark,setjet/spark,SnappyDataInc/spark,gengliangwang/spark,apache-spark-on-k8s/spark,debugger87/spark,UndeadBaneGitHub/spark,markhamstra/spark,caneGuy/spark,highfei2011/spark,JerryLead/spark,cin/spark,dhruve/spark,lvdongr/spark,skonto/spark,ahnqirage/spark,sureshthalamati/spark,dongjoon-hyun/spark,saturday-shi/spark,guoxiaolongzte/spark,yanboliang/spark,wangmiao1981/spark,bravo-zhang/spark,narahari92/spark,JoshRosen/spark,loneknightpy/spark,gengliangwang/spark,joseph-torres/spark,mahak/spark,alunarbeach/spark,sahilTakiar/spark,liutang123/spark,big-pegasus/spark,rikima/spark,guoxiaolongzte/spark,ptkool/spark,sahilTakiar/spark,ddna1021/spark,kissmetrics/spark,tengpeng/spark,jrshust/spark,chuckchen/spark,HyukjinKwon/spark,darionyaphet/spark,nilsgrabbert/spark,sureshthalamati/spark,wangyum/spark,tengpeng/spark,tengpeng/spark,apache-spark-on-k8s/spark,MLnick/spark,setjet/spark,jiangxb1987/spark,poffuomo/spark,poffuomo/spark,xuanyuanking/spark,nilsgrabbert/spark,kiszk/spark,lxsmnv/spark,highfei2011/spark,huang1900/spark,brad-kaiser/spark,liutang123/spark,WindCanDie/spark,map222/spark,byakuinss/spark,jiangxb1987/spark,adrian-ionescu/apache-spark,zuotingbing/spark,matthewfranglen/spark,1haodian/spark,wzhfy/spark,saltstar/spark,jkbradley/spark,publicRoman/spark,mzl9039/spark,facaiy/spark,alunarbeach/spark,SHASHANKB/spark,hvanhovell/spark,jiangxb1987/spark,rekhajoshm/spark,icexelloss/spark,MLnick/spark,SnappyDataInc/spark,xuanyuanking/spark,tejasapatil/spark,big-pegasus/spark,someorz/spark,mdespriee/spark,vinodkc/spark,WeichenXu123/spark,Aegeaner/spark,rekhajoshm/spark,ahnqirage/spark,brad-kaiser/spark,milliman/spark,skonto/spark,xflin/spark,icexelloss/spark,wzhfy/spark,guoxiaolongzte/spark,hhbyyh/spark,jkbradley/spark,narahari92/spark,taroplus/spark,hhbyyh/spark,map222/spark,holdenk/spark,chuckchen/spark,lxsmnv/spark,zero323/spark,spark-test/spark,aosagie/spark,WindCanDie/spark,andrewor14/spark,szhem/spark,kimoonkim/spark,ericvandenbergfb/spark,panfengfeng/spark,JerryLead/spark,MLnick/spark,zhouyejoe/spark,witgo/spark,hhbyyh/spark,shubhamchopra/spark,panfengfeng/spark,loneknightpy/spark,cloud-fan/spark,map222/spark,zzcclp/spark,gioenn/xSpark,dongjoon-hyun/spark,ueshin/apache-spark,pgandhi999/spark,ioana-delaney/spark,rikima/spark,sureshthalamati/spark,someorz/spark,gioenn/xSpark,xflin/spark,facaiy/spark,minixalpha/spark,ajaysaini725/spark,liutang123/spark,milliman/spark,zzcclp/spark,saturday-shi/spark,WindCanDie/spark,stanzhai/spark,liutang123/spark,yanboliang/spark,srowen/spark,dhruve/spark,ahnqirage/spark,srowen/spark,esi-mineset/spark,saturday-shi/spark,dbtsai/spark,rednaxelafx/apache-spark,michalsenkyr/spark,esi-mineset/spark,akopich/spark,narahari92/spark,LantaoJin/spark,ddna1021/spark,rezasafi/spark,skonto/spark,dongjoon-hyun/spark,mzl9039/spark,JerryLead/spark,jlopezmalla/spark,mdespriee/spark,jlopezmalla/spark,tengpeng/spark,HyukjinKwon/spark,panfengfeng/spark,kiszk/spark,icexelloss/spark,bravo-zhang/spark,aray/spark,ibm-research-ireland/sparkoscope,spark-test/spark,eyalfa/spark,wangmiao1981/spark,setjet/spark,ibm-research-ireland/sparkoscope,andrewor14/spark,nlalevee/spark,highfei2011/spark,hhbyyh/spark,minixalpha/spark,1haodian/spark,WeichenXu123/spark,WeichenXu123/spark,icexelloss/spark,goldmedal/spark,jrshust/spark,techaddict/spark,bdrillard/spark,joseph-torres/spark,nchammas/spark,szhem/spark,zuotingbing/spark,panfengfeng/spark,ahnqirage/spark,bravo-zhang/spark,ericvandenbergfb/spark,xflin/spark,mahak/spark,aray/spark,mike0sv/spark,stanzhai/spark,aray/spark,highfei2011/spark,rikima/spark,joseph-torres/spark,ptkool/spark,aokolnychyi/spark,spark-test/spark,zzcclp/spark,LantaoJin/spark,cin/spark,BryanCutler/spark,michalsenkyr/spark,tengpeng/spark,ericvandenbergfb/spark,cin/spark,dhruve/spark,loneknightpy/spark,sachintyagi22/spark,bdrillard/spark,witgo/spark,narahari92/spark,shubhamchopra/spark,bdrillard/spark,saturday-shi/spark,esi-mineset/spark,publicRoman/spark,bravo-zhang/spark,dbtsai/spark,kiszk/spark,kissmetrics/spark,zhouyejoe/spark,patrick-nicholson/spark,apache/spark,MLnick/spark,ConeyLiu/spark,wangyum/spark,Aegeaner/spark,jkbradley/spark,jianran/spark,mike0sv/spark,gengliangwang/spark,saltstar/spark,jiangxb1987/spark,narahari92/spark,BryanCutler/spark,esi-mineset/spark,chuckchen/spark,maropu/spark,shaneknapp/spark,holdenk/spark,yanboliang/spark,highfei2011/spark,akopich/spark,aray/spark,markhamstra/spark,yanboliang/spark,minixalpha/spark,ddna1021/spark,yanboliang/spark,wzhfy/spark,mike0sv/spark,darionyaphet/spark,taroplus/spark,shuangshuangwang/spark,lvdongr/spark,poffuomo/spark,metamx/spark,UndeadBaneGitHub/spark,rezasafi/spark,dbtsai/spark,cin/spark,darionyaphet/spark,goldmedal/spark,apache/spark,UndeadBaneGitHub/spark,JoshRosen/spark,goldmedal/spark,vinodkc/spark,bravo-zhang/spark,hvanhovell/spark,ajaysaini725/spark,akopich/spark,bdrillard/spark,BryanCutler/spark,ueshin/apache-spark,holdenk/spark,nchammas/spark,spark-test/spark,1haodian/spark,ioana-delaney/spark,stanzhai/spark,milliman/spark,mahak/spark,kissmetrics/spark,gengliangwang/spark,ioana-delaney/spark,MLnick/spark,minixalpha/spark,ibm-research-ireland/sparkoscope,big-pegasus/spark,cin/spark,WindCanDie/spark,ibm-research-ireland/sparkoscope,dongjoon-hyun/spark,jrshust/spark,ahnqirage/spark,milliman/spark,adrian-ionescu/apache-spark,huang1900/spark,holdenk/spark,aokolnychyi/spark,minixalpha/spark,holdenk/spark,ajaysaini725/spark,narahari92/spark,wangyum/spark,guoxiaolongzte/spark,bOOm-X/spark,szhem/spark,nchammas/spark,HyukjinKwon/spark,setjet/spark,WindCanDie/spark,lxsmnv/spark,rednaxelafx/apache-spark,shuangshuangwang/spark,jianran/spark,JoshRosen/spark,pgandhi999/spark,HyukjinKwon/spark,andrewor14/spark,techaddict/spark,xuanyuanking/spark,mzl9039/spark,shaneknapp/spark,caneGuy/spark,janewangfb/spark,xflin/spark,SHASHANKB/spark,caneGuy/spark,wangmiao1981/spark,tejasapatil/spark,xflin/spark,JoshRosen/spark,LantaoJin/spark,ConeyLiu/spark,tengpeng/spark,xflin/spark,brad-kaiser/spark,gioenn/xSpark,skonto/spark,JerryLead/spark,janewangfb/spark,jiangxb1987/spark,tejasapatil/spark,tejasapatil/spark,techaddict/spark,hvanhovell/spark,shaneknapp/spark,maropu/spark,jlopezmalla/spark,sahilTakiar/spark,SnappyDataInc/spark,taroplus/spark,shaneknapp/spark,xflin/spark,lxsmnv/spark,szhem/spark,poffuomo/spark,cloud-fan/spark,chuckchen/spark,sureshthalamati/spark,jianran/spark,ajaysaini725/spark,kiszk/spark,michalsenkyr/spark,facaiy/spark,debugger87/spark,sachintyagi22/spark,huang1900/spark,ron8hu/spark,vinodkc/spark,SHASHANKB/spark,lvdongr/spark,patrick-nicholson/spark,joseph-torres/spark,minixalpha/spark,kimoonkim/spark,akopich/spark,aosagie/spark,ron8hu/spark,aosagie/spark,shuangshuangwang/spark,zhouyejoe/spark,bOOm-X/spark,maropu/spark,rikima/spark,darionyaphet/spark,saturday-shi/spark,spark-test/spark,nilsgrabbert/spark,ConeyLiu/spark,liyichao/spark,jkbradley/spark,dhruve/spark,jlopezmalla/spark,nlalevee/spark,SHASHANKB/spark,darionyaphet/spark,shaneknapp/spark,mdespriee/spark,kissmetrics/spark,techaddict/spark,sachintyagi22/spark,MLnick/spark,ueshin/apache-spark,LantaoJin/spark,actuaryzhang/spark,facaiy/spark,HyukjinKwon/spark,adrian-ionescu/apache-spark,nlalevee/spark,dhruve/spark,bOOm-X/spark,zhouyejoe/spark,lvdongr/spark,sureshthalamati/spark,srowen/spark,saltstar/spark,highfei2011/spark,stanzhai/spark,someorz/spark,markhamstra/spark,brad-kaiser/spark,ioana-delaney/spark,ueshin/apache-spark,rednaxelafx/apache-spark,stanzhai/spark,bOOm-X/spark,darionyaphet/spark,facaiy/spark,publicRoman/spark,ConeyLiu/spark,apache/spark,ahnqirage/spark,rezasafi/spark,markhamstra/spark,markhamstra/spark,apache/spark,spark-test/spark,aokolnychyi/spark,ptkool/spark,BryanCutler/spark,goldmedal/spark,dhruve/spark,gioenn/xSpark,hhbyyh/spark,setjet/spark,mdespriee/spark,esi-mineset/spark,lvdongr/spark,rednaxelafx/apache-spark,actuaryzhang/spark,mzl9039/spark,minixalpha/spark,dhruve/spark,ueshin/apache-spark,aray/spark,jrshust/spark,gengliangwang/spark,goldmedal/spark,cloud-fan/spark,zuotingbing/spark,ron8hu/spark,rekhajoshm/spark,facaiy/spark,dbtsai/spark,WeichenXu123/spark,nchammas/spark,janewangfb/spark,caneGuy/spark,patrick-nicholson/spark,mahak/spark,ddna1021/spark,zero323/spark,SHASHANKB/spark,janewangfb/spark,mdespriee/spark,HyukjinKwon/spark,nilsgrabbert/spark,vinodkc/spark,metamx/spark,liyichao/spark,rezasafi/spark,nlalevee/spark,goldmedal/spark,milliman/spark,ptkool/spark,cin/spark,SnappyDataInc/spark,panfengfeng/spark,lxsmnv/spark,tejasapatil/spark,nlalevee/spark,metamx/spark,brad-kaiser/spark,alunarbeach/spark,actuaryzhang/spark,huang1900/spark,michalsenkyr/spark,maropu/spark,ddna1021/spark,highfei2011/spark,hhbyyh/spark,debugger87/spark,wzhfy/spark,sahilTakiar/spark,1haodian/spark,wangyum/spark,Aegeaner/spark,jrshust/spark,metamx/spark,ajaysaini725/spark,cloud-fan/spark,eyalfa/spark,sahilTakiar/spark,cloud-fan/spark,bdrillard/spark,mdespriee/spark,eyalfa/spark,markhamstra/spark,jrshust/spark,1haodian/spark,shaneknapp/spark,zzcclp/spark,hvanhovell/spark,akopich/spark,jiangxb1987/spark,WeichenXu123/spark,shubhamchopra/spark,srowen/spark,lxsmnv/spark,actuaryzhang/spark,bOOm-X/spark,michalsenkyr/spark,ConeyLiu/spark,zzcclp/spark,bravo-zhang/spark,kiszk/spark,rekhajoshm/spark,andrewor14/spark,mike0sv/spark,WeichenXu123/spark