[clang] [Clang][counted_by] Support casting the array to a different type (PR #136239)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

This seems pretty reasonable but I'd still like final sign off from @efriedma-quic or @rjmccall given it's codegen changes.

https://github.com/llvm/llvm-project/pull/136239