[llvm] [InstCombine] Canonicalize `switch(X << C)` into `switch(X)` (PR #77068)

[Joerg Sonnenberger via llvm-commits]

jsonn wrote:

I think it would make sense for the not-one-use case to check if the switch is dense enough for a jump table. In that case, the transformation should always be a win

https://github.com/llvm/llvm-project/pull/77068