[clang] Sort attributes according to source position before printing (PR #162556)

[Giuliano Belinassi via cfe-commits]

giulianobelinassi wrote:

> Can we use ~`llvm::partition`~ `llvm::stable_partition` to split `Attrs` into two parts by `.isValid()` so that we can use `llvm::sort`?
> 
> Please add a release note entry to clang/docs/ReleaseNotes.rst so that users can know the improvement.

I am not sure this is a good idea, once that will change the order of attributes with invalid source locations, which is something we may not want to. But let me try to see the consequences of it.

https://github.com/llvm/llvm-project/pull/162556