[llvm] [SimplifyCFG] Transform switch to select when common bits uniquely identify one case (PR #145233)

[Gábor Spaits via llvm-commits]

spaits wrote:

Thank you @antoniofrighetto @dtcxzyw . I think I have addressed everything. I have replaced `computeConstantRange` with `computeKnownBits` and removed the unused `ActiveBitsMask`.

https://github.com/llvm/llvm-project/pull/145233