[clang] [Clang] Implement the 'counted_by' attribute (PR #76348)

[Yeoul Na via cfe-commits]

https://github.com/rapidsna commented:

I left some comments. Looking good overall but `LocalDeclMap` doesn't seem to serve the purpose for this PR. And I'm not sure the code block using it would be actually necessary. Please see my inlined review.

https://github.com/llvm/llvm-project/pull/76348