QQmlIncubator can act synchronously when it's asked to create a component asynchronously if the QML engine has missing incubation controller.
It's typically not a problem because we get a QML engine from QQuickWindow or QQuickView, whose incubation controller is very smart.
On the other hand, Kirigami code relies on the fact that asynchronous QQmlIncubator will always act asynchronously. Otherwise it acts quite bad to the point where it hits an infinite recursion.
In order to make QtQuick based config modules work, this change adds a dummy incubation controller. It's not great, and we need to revisit whether having a shared qml engine is the right approach towards providing the support for QML based KCMs.