[clang] [clang] Unify `SourceLocation` and `IdentifierInfo*` pair-like data structures to `IdentifierLoc` (PR #135808)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

I REALLY like this.  I THINK this ends up being pretty trivial implementation for most of the files, and did a quick overlook on it, but please let another person or two do the scroll through to mkae sure I didnt miss anything.

https://github.com/llvm/llvm-project/pull/135808