[clang] [Clang] [Sema] Improve support for `__restrict`-qualified member functions (PR #83855)

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Sirraide wrote:

Sorry for the rather humongous pr description, but I tried to handle every edge case I could come up with (as well as include my rationale as to why I’ve decided to handle them that way)—thought it’s still possible that I missed some.

https://github.com/llvm/llvm-project/pull/83855