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

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

I think there was also a comment regarding updating/changing the name.

The current name may be confusing in some cases, as IIUC we do not require the described chain to actually be monotonic (i.e. check that it does not wrap)?

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