[llvm] [IVDescriptors] Implement MonotonicDescriptor (PR #214490)

[Gaëtan Bossu via llvm-commits]

https://github.com/gbossu commented:

I've only had a high level look. I think the analysis makes sense, but IMO the code structure makes it slightly harder than it needs to be.

https://github.com/llvm/llvm-project/pull/214490