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

[Erich Keane via cfe-commits]

erichkeane wrote:

> Both 1 and 2 seems like good options @hokein @erichkeane (especially 1 is probably something we should try to do)

I like 1, but not really 2, I think we should wait for this to be reasonably complete before merging it, particularly this close to the release.  I'd probably be ok with 2 if we wait a few weeks until after the release, so that we can deal with the fallout with less stress, and fix it before Clang21 release.

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