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

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

I think we should move towards tentative parsing as my comment under the previous PR suggests. I still think that the `SuppressAccessChecks` approach is not correct. We should teach the relevant tentative parsing logic to understand that we are defining an out of line constructor and tell us that's not a statement.

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