[clang] [clang][NFC] Move Bounds Safety Sema code to `SemaBoundsSafety.cpp` (PR #99330)

[Dan Liew via cfe-commits]

delcypher wrote:

@AaronBallman @Endilll Thanks for approving. I'll wait a bit for some of the code owners to chime in before landing this.

@rapidsna @hnrklssn @bwendling @kees Please let me know if you have any concerns about this refactor.

https://github.com/llvm/llvm-project/pull/99330