[clang] [NFC][analyzer] Extract general logic in security.ArrayBound (PR #210774)

[Balázs Benics via cfe-commits]

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

LGTM. thanks. This is how we operate. Clean, well-scoped patch.
Preserves bugs, and existing behavior.

https://github.com/llvm/llvm-project/pull/210774