[clang] [Clang] Implement C++26’s P2893R3 ‘Variadic friends’ (PR #101448)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Jens restored the suggested resolution in https://cplusplus.github.io/CWG/issues/2917.html and even put a date on it in case we need to reference it.

I also notified him that in our tests we are referring to proposed and suggested resolution by dates.
He also mentioned we can't rely on git history of https://github.com/cplusplus/CWG, because he's regularly squashing it. So if we think that something is wrong with CWG issue pages, we should bring this up to him instead of trying to cope using git history.

https://github.com/llvm/llvm-project/pull/101448