[clang] [Clang][Sema] Allow access to a public template alias declaration that refers to friend's private nested type (PR #83847)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

Did you intend for this to work as well: https://github.com/llvm/llvm-project/issues/41693#issuecomment-6118453780

https://github.com/llvm/llvm-project/pull/83847