[clang] [APINotes] Diagnose invalid Where.Parameters selectors (PR #209408)

[John Hui via cfe-commits]

https://github.com/j-hui commented:

I agree with the overall direction of these diagnostics and logic for actually emitting those diagnostics, but I'm having a hard time following the structure and implementation of `APINotesSelectorDiagnosticState` and `APINotesSelectorDiagnosticReaderState`. Those are "just" maintaining the state for which APINotes entries are actually used, right? If so, is it possible to encapsulate that logic a little more, or add some comments to clarify what is happening at a high level?



https://github.com/llvm/llvm-project/pull/209408