[clang] [BoundsSafety] WIP: Make 'counted_by' work for pointer fields; late parsing for 'counted_by' on decl attr position (PR #87596)

[Dan Liew via cfe-commits]

delcypher wrote:

@rapidsna I've put my version of this PR in my own pull request because when I edit the PR summary here it looks like you wrote it which is weird: https://github.com/llvm/llvm-project/pull/90786

https://github.com/llvm/llvm-project/pull/87596