Cleanup String tests
Cleanup String tests

Contributes to #6286

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