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

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

I really like the test coverage of this feature, but I started to wonder if we should start splitting up some sema tests into subfolders. I think the bounds-safety related tests would be a good candidate to have their own subfolder :)

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