[MLIR][Arith] Canonicalize cmpf(int to fp) to cmpi

Given a cmpf of either uitofp or sitofp and a constant, attempt to canonicalize it to a cmpi.

This PR rewrites equivalent code within LLVM to now apply to MLIR arith.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D117257