[clang] [Clang] Reject `this void` explicit object parameters (CWG2915) (PR #108817)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

> LGTM but it would be nice to do the other changes to cxx_dr_status as a separate (NFC) commit

We should always strive to keep unrelated changes separate. There are a lot of good reasons for this. The most basic is that if we have to revert then we lose both set of changes but clearly the unrelated DR documentation changes are NFC. 

https://github.com/llvm/llvm-project/pull/108817