Component could have attached property to query if component is completed

Sometimes it would be nice to know in QML if a component has finished being created. For example, onXXChanged handlers could be called before it is ready. Component attached property could perhaps be extended with some variable like isCompleted.

Or if that is not possible, perhaps QQuickItem::isComponentCompleted() could be exposed instead. Currently it is a protected member and not accessible from QML code.