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

[via cfe-commits]

antangelo wrote:

Thanks for the reviews!

>     * can you give a description  if what needs to be done in subsequent PRs? (maybe cxx_status.html should say "partial"
The remaining tasks are:
- Supporting dependent using-declarators such as `using Derived::Base::Base`. These are somewhat annoying to deal with, there isn't much of an existing mechanism (that I could find, at least) to look up the base type from the raw dependent identifier.
- Supporting deduction guides that are declared after the first lookup of deduction guides on the derived class. This is unimplemented due to a similar issue in alias template deduction that needs to be resolved first.

I have updated the cxx_status to partial, and added a note about the unsupported depdendent using-declarators. This aligns with the status for alias template deduction, which is partial due to the feature macro not being set. I presume the issue of deduction guides declared after the first lookup of deduction guides would be fixed in both features at the same time, either in this patch set if it is fixed in upstream first, or after this patch set as a followup.

>     * can you add a release notes
There should already be a clang release note, are there any other spots besides ReleaseNotes.rst and cxx_status.html that need updating?

>     * can you add PCH or module tests for the changes to ASTReader/ASTWriter?
I have added module tests that cover the feature.

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