[InstCombine] Add fold for redundant sign bits count comparison

For power-of-2 C:
((X s>> ShiftC) ^ X) u< C --> (X + C) u< (C << 1)
((X s>> ShiftC) ^ X) u> (C - 1) --> (X + C) u> ((C << 1) - 1)

(https://github.com/llvm/llvm-project/issues/56479)

Test plan:
0/ ninja check-llvm check-clang + bootstrap LLVM/Clang
1/ https://alive2.llvm.org/ce/z/eEUfx3

Differential revision: https://reviews.llvm.org/D130433