[instcombine] propagate single use freeze(gep inbounds X)

This is a follow on for D111675 which implements the gep case. I'd originally left it out because I was hoping to actually implement the inrange todo, but after a bit of staring at the code, decided to leave it as is since it doesn't effect this use case (i.e. instcombine requires the op to freeze to be an instruction).

Differential Revision: https://reviews.llvm.org/D111691