[clang] [clang]: reflection operator parsing for global namespace and primitive types (PR #164692)

[Erich Keane via cfe-commits]

erichkeane wrote:

FWIW: I'd MUCH rather we limit the scope of this as much as possible (and all followups).

Listing reflection as experimental, and leaving the 'not yet implementeds' in place are MUCH better idea than growing this already large patch. If reflection is 'experimental' anything we change that breaks serialization/etc is perfectly fine.

// TODO (reflection): is completely fine, we did it for concepts, so it would be great here too.

https://github.com/llvm/llvm-project/pull/164692