[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 You may want to close this PR but I'll leave this up to you.

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