[InstCombine] Fold gep of exact unsigned division (#82334)

Extend the transform added in
https://github.com/llvm/llvm-project/pull/76458 to also handle unsigned
division. X exact/ Y * Y == X holds independently of whether the
division is signed or unsigned.

Proofs: https://alive2.llvm.org/ce/z/wFd5Ec
(cherry picked from commit 26d4afc3)