[clang] [clang-tools-extra] [clang] improve class type sugar preservation in pointers to members (PR #130537)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This patch ended up being pretty massive... ANYTHING we can do to reduce the size of this would be very appreciated.

I DID NOT do more than a cursory look over the tests, so if someone else could do some work to make sure there isn't anything awkward/weird happening, I'd appreciate it.

Otherwise, I have some minor concerns/issues, but the code itself seems fine.

https://github.com/llvm/llvm-project/pull/130537