[clang] [Clang] Fix handling of pack indexing types in constraints of redeclaration (PR #139057)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 commented:

I think this LGTM in general, but please wait for some time in case @erichkeane @mizvekov have some ideas

https://github.com/llvm/llvm-project/pull/139057