Str::replace doesn't have caseSensitivity, whereas Str::remove does

[danielsimkus]

Hello,

Basically was just trying to Str::replace some stuff and we wanted it to be case-insensitive, I thought maybe there is a 3rd parameter for $caseSensitve like there is in Str::remove but there doesn't seem to be?

I'd be happy to make a PR for this if that's something you'd consider?