[clang] [clang-tools-extra] [Clang] Reland support friend declarations with a dependent nested-name-specifier (PR #208345)

[Oleksandr Tarasiuk via cfe-commits]

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a-tarasyuk wrote:

You’re right - my earlier answer was outdated. These changes should cover `CWG638`, so I’ve marked it as supported. 

https://github.com/llvm/llvm-project/pull/208345