[clang] [clang-tools-extra] Reland: [clang] NFC: Clear some uses of MemberPointerType::getClass (PR #132317)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

I'm going to go ahead and merge it, since this is such a small trivial and obviously correct fix for a relanding.

Otherwise, this blocks relanding a much bigger patch, which is a rebase burden.

We can always make amendments post commit if anyone feels like it.

https://github.com/llvm/llvm-project/pull/132317