[SPARK-14152][ML][PYSPARK] MultilayerPerceptronClassifier supports save/load for Python API
[SPARK-14152][ML][PYSPARK] MultilayerPerceptronClassifier supports save/load for Python API

## What changes were proposed in this pull request?
```MultilayerPerceptronClassifier``` supports save/load for Python API.

## How was this patch tested?
doctest.

cc mengxr jkbradley yinxusen

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #11952 from yanboliang/spark-14152.

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