[clang] [clang-repl] Allow private type aliases in out-of-line member function return types (PR #178842)

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fogsong233 wrote:

See https://github.com/llvm/llvm-project/blob/main/clang/lib/Parse/ParseDecl.cpp#L3643-L3673
It is the access logic in `ParseDeclarationOrFunctionDefinition`, which will be neglected if the token is changed previously.

https://github.com/llvm/llvm-project/pull/178842