[llvm] [SCEV] Introduce IncrementNSUW, replacing NSSW (PR #219559)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

So, I think NSUW is a refinement and weakening of NSSW that is useful when we can prove that the step is known-non-negative, similar to the way NUSW is a refinement and weakening of NUUW that is useful when we can prove that the start is known-non-negative.

https://github.com/llvm/llvm-project/pull/219559