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

[Erich Keane via cfe-commits]

erichkeane wrote:

> I'll go ahead and revert the commit for now. My local test run has just finished with no new errors. Feel free to recommit with the new test cases and the fix.

Doing a revert like this during our release process is actually quite a disturbance, particularly when the committer is actively working on the fix (and has identified it!).  In the future please give them a chance to fix it before reverting on them.

ALSO, in the future, if you are going to do a revert while we are in a release process, you need to make sure to submit a request to revert it from the release branch at the same time, you cannot just revert in 'main'.

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