[clang] [clang-tools-extra] [clang] Initialize pattern TypeLoc of PackIndexingTypeLoc (PR #231191)

[via cfe-commits]

max-winkler wrote:

> I filed #232194 for the TypeLoc issue
> 
> Note that I didn't touch the RecursiveASTVisitor part and I hope you can continue completing this PR after the TypeLoc one gets fixed :)

Thanks for the quick fix of the `PackIndexingTypeLoc`. I fetched your branch and set my tests and the fix in RecursiveASTVisitor on top of it:
- All tests (`RecursiveASTVisitorTests` of clang and `TargetDeclTest.PackIndexing`) of clangd) pass
- The ellipsis location is correct in `T...[0] x` and `using U=T...[0]`
- The change in `RecursiveASTVisitor` is indeed necessary, as you pointed out already.

I understand the necessity of a correct initialization of the `PackIndexingTypeLoc` in the parser now.

I will reduce my PR to the fix in `RecursiveASTVisitor` + the test cases.

https://github.com/llvm/llvm-project/pull/231191