Have IList and non-IList versions of all Enumerable.Skip tests.
Have IList and non-IList versions of all Enumerable.Skip tests.

#4551 introduced optimised versions of Skip for IList<T> sources. Have all
tests for Skip test both this and the previous path.

nbarbettini/corefx,YoupHulsebos/corefx,dsplaisted/corefx,ericstj/corefx,ellismg/corefx,ellismg/corefx,YoupHulsebos/corefx,benpye/corefx,Chrisboh/corefx,ellismg/corefx,richlander/corefx,Jiayili1/corefx,richlander/corefx,alexperovich/corefx,billwert/corefx,mafiya69/corefx,benjamin-bader/corefx,ViktorHofer/corefx,yizhang82/corefx,tijoytom/corefx,dotnet-bot/corefx,jhendrixMSFT/corefx,rubo/corefx,rahku/corefx,ravimeda/corefx,axelheer/corefx,khdang/corefx,shimingsg/corefx,cartermp/corefx,lggomez/corefx,weltkante/corefx,richlander/corefx,SGuyGe/corefx,benjamin-bader/corefx,manu-silicon/corefx,elijah6/corefx,cydhaselton/corefx,wtgodbe/corefx,shahid-pk/corefx,cydhaselton/corefx,dhoehna/corefx,yizhang82/corefx,cydhaselton/corefx,wtgodbe/corefx,Petermarcu/corefx,Petermarcu/corefx,weltkante/corefx,elijah6/corefx,alphonsekurian/corefx,stone-li/corefx,stephenmichaelf/corefx,ericstj/corefx,josguil/corefx,the-dwyer/corefx,lggomez/corefx,jhendrixMSFT/corefx,mazong1123/corefx,cartermp/corefx,JosephTremoulet/corefx,billwert/corefx,janhenke/corefx,parjong/corefx,rubo/corefx,rubo/corefx,mellinoe/corefx,wtgodbe/corefx,the-dwyer/corefx,benpye/corefx,benjamin-bader/corefx,elijah6/corefx,shahid-pk/corefx,krytarowski/corefx,SGuyGe/corefx,DnlHarvey/corefx,ellismg/corefx,stone-li/corefx,krk/corefx,benjamin-bader/corefx,Ermiar/corefx,zhenlan/corefx,parjong/corefx,dotnet-bot/corefx,rahku/corefx,khdang/corefx,janhenke/corefx,dhoehna/corefx,nbarbettini/corefx,krytarowski/corefx,marksmeltzer/corefx,krk/corefx,stephenmichaelf/corefx,ViktorHofer/corefx,MaggieTsang/corefx,pallavit/corefx,axelheer/corefx,marksmeltzer/corefx,stone-li/corefx,ravimeda/corefx,DnlHarvey/corefx,shmao/corefx,seanshpark/corefx,alexperovich/corefx,nbarbettini/corefx,fgreinacher/corefx,JosephTremoulet/corefx,pallavit/corefx,zhenlan/corefx,seanshpark/corefx,josguil/corefx,nchikanov/corefx,alphonsekurian/corefx,nbarbettini/corefx,SGuyGe/corefx,parjong/corefx,dotnet-bot/corefx,mellinoe/corefx,weltkante/corefx,nbarbettini/corefx,krytarowski/corefx,khdang/corefx,tstringer/corefx,iamjasonp/corefx,the-dwyer/corefx,ptoonen/corefx,shimingsg/corefx,krytarowski/corefx,stephenmichaelf/corefx,rahku/corefx,MaggieTsang/corefx,weltkante/corefx,ViktorHofer/corefx,rjxby/corefx,MaggieTsang/corefx,YoupHulsebos/corefx,dotnet-bot/corefx,gkhanna79/corefx,rahku/corefx,Chrisboh/corefx,marksmeltzer/corefx,Petermarcu/corefx,MaggieTsang/corefx,benpye/corefx,janhenke/corefx,tijoytom/corefx,dotnet-bot/corefx,shahid-pk/corefx,the-dwyer/corefx,janhenke/corefx,gkhanna79/corefx,shimingsg/corefx,krytarowski/corefx,nbarbettini/corefx,kkurni/corefx,shimingsg/corefx,ellismg/corefx,axelheer/corefx,rubo/corefx,parjong/corefx,shahid-pk/corefx,Chrisboh/corefx,benjamin-bader/corefx,seanshpark/corefx,pallavit/corefx,jcme/corefx,Ermiar/corefx,mmitche/corefx,billwert/corefx,alexperovich/corefx,pallavit/corefx,ViktorHofer/corefx,Jiayili1/corefx,lggomez/corefx,pallavit/corefx,jhendrixMSFT/corefx,zhenlan/corefx,josguil/corefx,rahku/corefx,alphonsekurian/corefx,marksmeltzer/corefx,DnlHarvey/corefx,billwert/corefx,mellinoe/corefx,tstringer/corefx,rjxby/corefx,tstringer/corefx,cydhaselton/corefx,axelheer/corefx,nchikanov/corefx,DnlHarvey/corefx,Jiayili1/corefx,ravimeda/corefx,dhoehna/corefx,the-dwyer/corefx,tijoytom/corefx,iamjasonp/corefx,benjamin-bader/corefx,janhenke/corefx,shmao/corefx,mazong1123/corefx,axelheer/corefx,alexperovich/corefx,jlin177/corefx,cydhaselton/corefx,kkurni/corefx,gkhanna79/corefx,elijah6/corefx,alphonsekurian/corefx,mazong1123/corefx,mmitche/corefx,alphonsekurian/corefx,billwert/corefx,shmao/corefx,mazong1123/corefx,shimingsg/corefx,rubo/corefx,seanshpark/corefx,mazong1123/corefx,ericstj/corefx,weltkante/corefx,wtgodbe/corefx,mafiya69/corefx,Priya91/corefx-1,alexperovich/corefx,adamralph/corefx,benpye/corefx,fgreinacher/corefx,kkurni/corefx,parjong/corefx,pallavit/corefx,yizhang82/corefx,stone-li/corefx,YoupHulsebos/corefx,alexperovich/corefx,the-dwyer/corefx,manu-silicon/corefx,josguil/corefx,wtgodbe/corefx,khdang/corefx,richlander/corefx,shmao/corefx,rahku/corefx,twsouthwick/corefx,gkhanna79/corefx,yizhang82/corefx,ViktorHofer/corefx,tijoytom/corefx,SGuyGe/corefx,mazong1123/corefx,ViktorHofer/corefx,ptoonen/corefx,mafiya69/corefx,adamralph/corefx,parjong/corefx,cartermp/corefx,Petermarcu/corefx,shimingsg/corefx,mazong1123/corefx,Petermarcu/corefx,mmitche/corefx,Jiayili1/corefx,benpye/corefx,wtgodbe/corefx,billwert/corefx,shmao/corefx,mafiya69/corefx,seanshpark/corefx,JosephTremoulet/corefx,cartermp/corefx,gkhanna79/corefx,Priya91/corefx-1,lggomez/corefx,benpye/corefx,seanshpark/corefx,cartermp/corefx,mokchhya/corefx,ptoonen/corefx,stephenmichaelf/corefx,manu-silicon/corefx,gkhanna79/corefx,krk/corefx,josguil/corefx,iamjasonp/corefx,Priya91/corefx-1,krk/corefx,kkurni/corefx,rjxby/corefx,DnlHarvey/corefx,DnlHarvey/corefx,shimingsg/corefx,dsplaisted/corefx,marksmeltzer/corefx,elijah6/corefx,SGuyGe/corefx,tijoytom/corefx,rjxby/corefx,jhendrixMSFT/corefx,ravimeda/corefx,dhoehna/corefx,yizhang82/corefx,Chrisboh/corefx,jhendrixMSFT/corefx,dotnet-bot/corefx,jhendrixMSFT/corefx,jlin177/corefx,kkurni/corefx,iamjasonp/corefx,marksmeltzer/corefx,jcme/corefx,manu-silicon/corefx,Jiayili1/corefx,yizhang82/corefx,twsouthwick/corefx,BrennanConroy/corefx,nchikanov/corefx,nchikanov/corefx,tstringer/corefx,billwert/corefx,fgreinacher/corefx,ravimeda/corefx,dsplaisted/corefx,Ermiar/corefx,YoupHulsebos/corefx,rjxby/corefx,ericstj/corefx,cydhaselton/corefx,jlin177/corefx,Priya91/corefx-1,krytarowski/corefx,Chrisboh/corefx,JosephTremoulet/corefx,mmitche/corefx,mmitche/corefx,yizhang82/corefx,ptoonen/corefx,mokchhya/corefx,weltkante/corefx,ericstj/corefx,richlander/corefx,JosephTremoulet/corefx,jcme/corefx,lggomez/corefx,axelheer/corefx,jcme/corefx,parjong/corefx,Priya91/corefx-1,Ermiar/corefx,lggomez/corefx,ravimeda/corefx,krytarowski/corefx,shahid-pk/corefx,elijah6/corefx,JosephTremoulet/corefx,shmao/corefx,YoupHulsebos/corefx,elijah6/corefx,krk/corefx,twsouthwick/corefx,Ermiar/corefx,jcme/corefx,zhenlan/corefx,dotnet-bot/corefx,JosephTremoulet/corefx,Priya91/corefx-1,iamjasonp/corefx,mokchhya/corefx,manu-silicon/corefx,cydhaselton/corefx,jlin177/corefx,ericstj/corefx,kkurni/corefx,nchikanov/corefx,zhenlan/corefx,krk/corefx,tijoytom/corefx,mmitche/corefx,gkhanna79/corefx,alexperovich/corefx,Petermarcu/corefx,mafiya69/corefx,mellinoe/corefx,manu-silicon/corefx,nchikanov/corefx,Ermiar/corefx,Petermarcu/corefx,stone-li/corefx,manu-silicon/corefx,richlander/corefx,rjxby/corefx,MaggieTsang/corefx,alphonsekurian/corefx,nbarbettini/corefx,stephenmichaelf/corefx,jlin177/corefx,dhoehna/corefx,alphonsekurian/corefx,BrennanConroy/corefx,cartermp/corefx,seanshpark/corefx,ptoonen/corefx,Jiayili1/corefx,YoupHulsebos/corefx,twsouthwick/corefx,BrennanConroy/corefx,adamralph/corefx,Chrisboh/corefx,weltkante/corefx,MaggieTsang/corefx,tstringer/corefx,nchikanov/corefx,ellismg/corefx,rahku/corefx,stone-li/corefx,marksmeltzer/corefx,ViktorHofer/corefx,fgreinacher/corefx,MaggieTsang/corefx,zhenlan/corefx,wtgodbe/corefx,dhoehna/corefx,Jiayili1/corefx,tstringer/corefx,krk/corefx,jlin177/corefx,shmao/corefx,mellinoe/corefx,mokchhya/corefx,khdang/corefx,richlander/corefx,iamjasonp/corefx,the-dwyer/corefx,iamjasonp/corefx,mafiya69/corefx,mellinoe/corefx,SGuyGe/corefx,DnlHarvey/corefx,janhenke/corefx,ericstj/corefx,Ermiar/corefx,shahid-pk/corefx,rjxby/corefx,ravimeda/corefx,stone-li/corefx,lggomez/corefx,stephenmichaelf/corefx,twsouthwick/corefx,twsouthwick/corefx,zhenlan/corefx,dhoehna/corefx,ptoonen/corefx,khdang/corefx,stephenmichaelf/corefx,tijoytom/corefx,mokchhya/corefx,josguil/corefx,jhendrixMSFT/corefx,jcme/corefx,jlin177/corefx,twsouthwick/corefx,ptoonen/corefx,mokchhya/corefx,mmitche/corefx