[clang] [clang] CTAD: implement the missing IsDeducible constraint for alias templates (PR #89358)

[Haojian Wu via cfe-commits]

hokein wrote:

Thanks for the review.

> I'll approve that modulo nit but i think we want
> 
> * An issue to keep track of the duplication in `FinishTemplateArgumentDeduction`

Filed #92224.

> * A follow up PR to improve diagnostics

Filed #92225, and assigned to myself. Will do it.

> Thanks!



https://github.com/llvm/llvm-project/pull/89358