[clang] [APINotes] Add Where.Object selectors for C++ methods (PR #216148)

[via cfe-commits]

StoeckOverflow wrote:

Thanks for forwarding these notes. I pushed an update addressing all four points:

- Removed the unused `FunctionTableKey` constructors.
- Folded `formatAPINotesFunctionSelector` into `FunctionSelector::format()`.
- Renamed the local variable shadowing `FunctionObjectSelector::Ref`.
- Simplified the ref-qualifier flag assertion.

I also removed temporary copies when constructing and deserializing function selector keys and restored the parameter-ID vector’s previous inline capacity.

https://github.com/llvm/llvm-project/pull/216148