[clang] [Bounds-Safety] Add sized_by, counted_by_or_null & sized_by_or_null (PR #93231)

[Dan Liew via cfe-commits]

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

Thanks for addressing my comment. I have some nits but I'll leave it to your discretion whether or not you fix them.

https://github.com/llvm/llvm-project/pull/93231