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

[via cfe-commits]

cor3ntin wrote:

we are implementing the proposed resolution, which is the second set of change in that issue. we should *not* implement the "suggested resolution" as discussions are still ongoing (notably concerns of it being too restrictive).

Just updating the date is fine

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