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

[Aaron Ballman via cfe-commits]

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

There are a few minor suggestions from @delcypher that should be addressed, but overall the changes LGTM (assuming there are no precommit CI surprises after fixing the merge conflicts).

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