[clang] [Bounds Safety][NFC] Add `SemaBoundsSafety` class and move existing Sema checks there (PR #98954)

[Henrik G. Olsson via cfe-commits]

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

LGTM, might want to give the rest some time to have a look though

https://github.com/llvm/llvm-project/pull/98954