[clang] [clang] Implement P2582R1: CTAD from inherited constructors (PR #98788)

[Haojian Wu via cfe-commits]

hokein wrote:

We seem to have lost track of this. This patch has been around for a while, and it needs a rebase before it can be merged.

>From what I can tell, part 1 splitting out deduction guide source tracking has already landed, and the missing piece for alias templates (#103016) is done as well. I think we can probably mark P1814 as "done" in the C++ status page, even though there are still some opening issues.

The clang 21 branch will be cut next week. Given the current state of this patch and the remaining issues, I don’t think it’s ready to be merged in time for the release. My take would be to merge it after the branch cut and continue polishing it afterward. Not sure if @antangelo has time to work on it at the moment.

https://github.com/llvm/llvm-project/pull/98788