[libcxx] [clang] [SemaCXX] Implement CWG2137 (list-initialization from objects of the same type) (PR #77768)

[via cfe-commits]

alexfh wrote:

Actually, on the second look it doesn't seem to be too ambiguous to me. I *think* `std::vector<A>` should be a strictly better match in this case.

https://github.com/llvm/llvm-project/pull/77768