[llvm] [Support] Adding fast-path for KnownBits's udiv when RHS is constant (PR #189779)

[Max Graey via llvm-commits]

MaxGraey wrote:

> You could also add a matching overload shl(KnownBits, unsigned)

Makes sense. Let's do it before merging

https://github.com/llvm/llvm-project/pull/189779