[Macros] Improve visitation of auxiliary decls

Use the same pattern as 'getAllMembers()'. This supports nested macro
expansion:
```
std::function<void(Decl *)> visit;
visit = [&](Decl *d) {
  doIt(d);
  d->visitAuxiliaryDecls(visit);
};
for (auto *d : decls)
  visit(d);
```

Don't visit auxiliary decls in `PrintAST::visit(Decl *)` this function
is only intended for single decl printing. The caller should visit them
separately. For that, add
`ModuleDecl::getTopLevelDeclsWithAuxiliaryDecls()`

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -833,7 +833,7 @@ bool swift::emitSwiftInterface(raw_ostream &out,
   InheritedProtocolCollector::PerTypeMap inheritedProtocolMap;
 
   SmallVector<Decl *, 16> topLevelDecls;
-  M->getTopLevelDecls(topLevelDecls);
+  M->getTopLevelDeclsWithAuxiliaryDecls(topLevelDecls);
   for (const Decl *D : topLevelDecls) {
     InheritedProtocolCollector::collectProtocols(inheritedProtocolMap, D);