[clang] [Clang][P1061] Add stuctured binding packs (PR #121417)

[Erich Keane via cfe-commits]

erichkeane wrote:

> The code and test coverage looks good. There are a couple of comments that have not been addressed.
> 
> And there is @zygoloid suggestion to generalize `SubstNonTypeTemplateParmPackExpr` - do we want to do that now or address it after the fact?
> 
> Maybe trying to land that today is not the brightest idea. However, we should target to have it landed before rc2 or something like that We'd make a lot of folks happy having that in 20, I think. And while the PR is not tiny, it's seems also fairly low risk (famous last words!)
> 
> @erichkeane @AaronBallman @Sirraide

Yeah, I think I agree.  I don't see much risk here besides this feature being broken, which I'm OK with.


https://github.com/llvm/llvm-project/pull/121417