ExtensionSystem: Move away from QList

Qt 6 API will move away from it.
Use QVector for API and some std container for internal things.

Change-Id: Iff14d48a47d5ac52ade875d9c8c84ad8a4f577d8
Reviewed-by: hjk <hjk@qt.io>

src/plugins/cppeditor/cppeditorplugin.cpp

@@ -371,11 +371,9 @@ void CppEditorPluginPrivate::inspectCppCodeModel()
 }
 
 #ifdef WITH_TESTS
-QList<QObject *> CppEditorPlugin::createTestObjects() const
+QVector<QObject *> CppEditorPlugin::createTestObjects() const
 {
-    return QList<QObject *>()
-        << new Tests::DoxygenTest
-        ;
+    return {new Tests::DoxygenTest};
 }
 #endif