[clang] [libcxx] [Clang] Implement CWG2137 (list-initialization from objects of the same type) (PR #94355)

[Mital Ashok via cfe-commits]

MitalAshok wrote:

@yxsamliu Re: https://github.com/llvm/llvm-project/pull/77768#issuecomment-1957171805: That is the expected behaviour, since CWG2137 expressly wants to use initializer_list constructors over non-initializer_list constructors (especially copy constructors)

https://github.com/llvm/llvm-project/pull/94355