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/clangcodemodel/clangcodemodelplugin.h

@@ -58,7 +58,7 @@ private:
     ::Utils::ParameterAction *m_generateCompilationDBAction = nullptr;
     QFutureWatcher<Utils::GenerateCompilationDbResult> m_generatorWatcher;
 #ifdef WITH_TESTS
-    QList<QObject *> createTestObjects() const override;
+    QVector<QObject *> createTestObjects() const override;
 #endif
 };