[clang] [Sema]Substitue parameter packs when deduced from function parameter (PR #79371)

[Gábor Spaits via cfe-commits]

spaits wrote:

Thank you @cor3ntin for reviewing my PR.

I addressed all of your comments.

- I fixed the types.
- I added support for deduction of non-trailing packs when there is no separator type.
- Simplified the code. This simplification has affect on the code you asked about.

Could you please review my recent changes?

https://github.com/llvm/llvm-project/pull/79371