[clang] Reland: [clang] unified CWG2398 and P0522 changes; finishes implementation of P3310 (PR #124137)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> Can you explain the revert-issue, and what you did to fix it? The github diff is making REALLY difficult to understand what you did..

If you go on the commit list, you can click on the commit which I pointed out in the OP ([clang] Changes to template argument list checking", which contains the changes which fix the revert-causing issue)

The commit message there has explanation of the fix.

https://github.com/llvm/llvm-project/pull/124137