[clang] Rework the printing of attributes (PR #87281)

[Erich Keane via cfe-commits]

erichkeane wrote:

> A note from left field: I think this PR broke the IWYU test suite. We use `TemplateDecl::print` + some postprocessing to generate template forward-declarations. We're seeing this diff now:
> 
> ```diff
> -template <typename T> class FinalTemplate;
> +template <typename T> class  FinalTemplate;
> ```
> 
> So a spurious extra space.
> 
> We would be grateful if this _didn't_ make the 18.x branches, because we've already released an 18.x-compatible version of IWYU, and it would be a shame if that release had a failing test suite when built against later 18.x Clang.
> 
> I'll work around this on our latest mainline.

Ooof, I think that DOES decide it for me.  @vgvassilev : can you look into that extra space to see if you can track it down?  

https://github.com/llvm/llvm-project/pull/87281