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

[Gábor Horváth via cfe-commits]

https://github.com/Xazax-hun commented:

Overall, looks great! But I wonder if it would be possible to simplify some parts a little bit further. It is great that all the quadratic parts are gone now. 

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