[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=7c265e9f576041c20422218571bc2dacf20d65d9&to=bbe3c19fea298183e1d35e7f56f264c5ae386ad1&stat=instructions:u

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