Generated interfaces for Clang modules used to try printing normal
comments between decls extracted from the header text. That was because
doc-comment was not common in C/ObjC headers. But mainly because of
"import as member feature" Clang decls aren't printed in the order as
they appear in the header file, the logic determinig which comment
belongs to which decl was not working property. We've decided to remove
that feature and only print the proper doc-comments as it has been
getting common.
rdar://93731287
This reapplies f1c48daf70 with the test split up so that the
availability bits don't affect other platforms.
Seen as @available attributes being printed with "_" in interface
generation, but fixing it in the importer means they can't leak into
anywhere else.
rdar://problem/30451293
