[clang] [llvm] Expose format (attribute) info for function declarations in Clang Index API (PR #113754)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll commented:

I'm sorry it took us a while to notice this PR.

I think that documentation of new functions should describe what happens on unhappy code paths, too.

I also would like to see unit tests and a release note.

Even more, I'd like @AaronBallman to sign this off when he comes back (mid-January), because this is about the first time we add functions to CIndex API that are specific to a particular attribute. The approach seems fine to me, but CIndex is our stable API, so I prefer us to move slowly here.

https://github.com/llvm/llvm-project/pull/113754