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

[Dan Liew via cfe-commits]

delcypher wrote:

@Xazax-hun This is something I'd like too. Unfortunately in previous discussions we were asked to not do this.
https://github.com/llvm/llvm-project/pull/70480#discussion_r1379166020
https://github.com/llvm/llvm-project/pull/70480#discussion_r1377966526

As the number of tests grow I think it will become more justfiable to put Bounds Safety tests in their own folder.

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