[clang] [clang] Implement a bitwise_copyable builtin type trait. (PR #86512)

[Ilya Biryukov via cfe-commits]

https://github.com/ilya-biryukov requested changes to this pull request.

Could we rewrite the description and documentation to capture what the type trait is doing now?
We have a lot of references to the `is_trivially_copyable`, which is almost fully irrelevant to the current implementation. 

Also, is there a *simple* way to make this work with the corresponding sanitizer?
If not or it requires too much work, we could definitely return false here. Just making sure we explored this.

https://github.com/llvm/llvm-project/pull/86512