[InstCombine] Preserve nuw/nsw/exact flags when transforming (C shift (A add...

[InstCombine] Preserve nuw/nsw/exact flags when transforming (C shift (A add nuw C1)) --> ((C shift C1) shift A). (#79490)

If we weren't shifting out any non-zero bits or changing the sign before the transform, we
shouldn't be after.

Alive2: https://alive2.llvm.org/ce/z/mB-rWz