Optimize string.Replace(char, char)
Optimize string.Replace(char, char)

Returns the same string if they're the same.

Related PR in CoreCLR: dotnet/coreclr#3221
manu-silicon/corert,botaberg/corert,gregkalapos/corert,shrah/corert,manu-silicon/corert,kyulee1/corert,sandreenko/corert,kyulee1/corert,schellap/corert,yizhang82/corert,schellap/corert,botaberg/corert,krytarowski/corert,mjp41/corert,tijoytom/corert,yizhang82/corert,mjp41/corert,gregkalapos/corert,sandreenko/corert,mjp41/corert,krytarowski/corert,krytarowski/corert,yizhang82/corert,mjp41/corert,mjp41/corert,manu-silicon/corert,krytarowski/corert,shrah/corert,gregkalapos/corert,kyulee1/corert,shrah/corert,sandreenko/corert,tijoytom/corert,kyulee1/corert,schellap/corert,schellap/corert,gregkalapos/corert,tijoytom/corert,schellap/corert,botaberg/corert,manu-silicon/corert,yizhang82/corert,sandreenko/corert,tijoytom/corert,shrah/corert,botaberg/corert,manu-silicon/corert