[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=f6c8e7dc3e1cbcecc2f01d898b895b96bb5723be&to=3879271a9f54e26d50948dc16b1b2ed0d0210431&stat=instructions:u

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