[CodeCompletion] Complete Swift only module name after 'import'

rdar://problem/39392446

lib/Frontend/ParseableInterfaceModuleLoader.cpp

@@ -1377,3 +1377,10 @@ bool ParseableInterfaceModuleLoader::buildSwiftModuleFromSwiftInterface(
   return builder.buildSwiftModule(OutPath, /*shouldSerializeDeps*/true,
                                   /*ModuleBuffer*/nullptr);
 }
+
+void ParseableInterfaceModuleLoader::collectVisibleTopLevelModuleNames(
+    SmallVectorImpl<Identifier> &names) const {
+  collectVisibleTopLevelModuleNamesImpl(
+      names,
+      file_types::getExtension(file_types::TY_SwiftParseableInterfaceFile));
+}