[Interest] QML/C++ interaction in Qt6

[Ulf Hermann]

> - Allow QML to access public properties of classes, even if these public 
> properties do not use `Q_PROPERTY`
> - Allow QML access to classes that are neither `QObject`, nor `QGadget`

This is not planned right now. Note that we rely on moc to generate the 
class descriptions that QML uses. Therefore, we need constructs like 
Q_OBJECT, Q_GADGET and Q_PROPERTY to make things visible.

best regards,
Ulf