Some macro-generated declarations are not being printed in the
Obj-C/C++ generated header. Members introduced by attached `member`
macros on a type appear to be fine, but those introduced by a
attached `peer` or freestanding `declaration` macros don't show up.
This change updates the header writer to call `getAllMembers`
throughout instead of `getMembers`, which makes sure that everything
gets collected. Likewise, we update the top-level logic from
`getTopLevelDecls` to `getTopLevelDeclsWithAuxiliaryDecls` to pick
up freestanding decls introduced at file scope.
Fixes https://github.com/swiftlang/swift/issues/68170.
