[clang] [CIR] Add PointerLikeType interface support for cir::PointerType (PR #139768)

[Erich Keane via cfe-commits]

erichkeane wrote:

> @razvanlupusoru and @erichkeane Are you OK with committing this now?

I am if @razvanlupusoru is.  It'll probably take me a pretty decent amount of time to figure out if this is good enough for my uses, so I'd rather have it done now and fixup later if necessary.

https://github.com/llvm/llvm-project/pull/139768