[clang] [clang] associate newline and function decl. trailing Doxygen comments (PR #198534)

[Aydın Mercan via cfe-commits]

aydinmercan wrote:

> This change would need tests. Thanks

On it!

Oh BTW I was meaning the ask but in the comment annotation test [same-line trailing function comments are asserted to not be attached](https://github.com/llvm/llvm-project/blob/main/clang/test/Index/annotate-comments.cpp#L98-L102). The commit in blame doesn't give a reason why it is restricted, by chance do you know the reasoning behind it? Thanks! @cor3ntin

https://github.com/llvm/llvm-project/pull/198534