[IR] Replace *all* uses of a constant expression by corresponding instruction

When a constant expression CE is being converted into a corresponding instruction I,
CE is supposed to be replaced by I. However, it is possible that CE is being used multiple
times within a parent instruction PI. Make sure that *all* the uses of CE within PI are
replaced by I.

Reviewed By: rampitec, arsenm

Differential Revision: https://reviews.llvm.org/D112717