[clang] [clang] Handle template argument conversions for non-pack param to pack argument (PR #110963)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

I admittedly don't have a great idea of what is going on here, but I don't see anything glaringly out of place, so +1.

https://github.com/llvm/llvm-project/pull/110963