Emit single named return type with adornments

Put it through `print_to_string`, which unlike `.to_string` also adds `cpp2::` qualifications for names like `i164`.

Author: hsutter

source/to_cpp1.h

@@ -5784,7 +5784,7 @@ class cppfront
                     printer.print_extra(
                         "\nusing "
                         + func_name + "_ret = "
-                        + r->parameters[0]->declaration->get_object_type()->to_string()
+                        + print_to_string( *r->parameters[0]->declaration->get_object_type() )
                         + ";"
                     );
                 }