[llvm] [DAG] Replace getValid*ShiftAmountConstant helpers with getValid*ShiftAmount helpers to support KnownBits analysis (PR #93182)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

https://llvm-compile-time-tracker.com/compare.php?from=84729c9df30b29d5f4e903ad71235a6aa0c764d6&to=d8ee31077ae6f1acea83c786d9d1835301d44877&stat=instructions:u

https://github.com/llvm/llvm-project/pull/93182