Add information about problematic object to warning message

Otherwise it's rather impossible to find the issue in the QML code.

Change-Id: I894886feb58864503e6ffd2dd28626e68d623aae
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/qml/qml/qqmlcomponent.cpp

@@ -1377,8 +1377,7 @@ static void QQmlComponent_setQmlParent(QObject *me, QObject *parent)
             }
         }
         if (needParent)
-            qWarning("QQmlComponent: Created graphical object was not "
-                     "placed in the graphics scene.");
+            qmlWarning(me) << "Created graphical object was not placed in the graphics scene.";
     }
 }