[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=ebc6c28a252915e6689ba7559bdc17eed0eea10c&to=9ced5e9548273789dc132ec033a31385ef429a21&stat=instructions:u

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