Make it possible to embed a Qt Quick View inside a QLayout

Suppose we have the following UI hierarchy:

QWidget ['widget']  (has a QHBoxLayout)
  QWidget ['windowContainer']. (Added to the QHBoxLayout)
    QQuickWindow
      QQuickItem ['rootItem']

If a developer is embedding a QQuickWindow inside a QLayout there are some expectations that we should try to meet:

1. Sensible size hints and size policies are propagated from the QQuickWindow up to the QLayout (actually it should be enough to propagate it up to the "windowContainer" widget.
   • If this works, the initial size of the 'widget' QWidget should be derived from the size of the 'rootItem'
   • Remember that size hints includes both min,preferred and max size.
   • Resizing the 'widget' might cause the QQuickWindow to be resized.
   • How can size policies be communicated up from the 'rootItem' and to the 'windowContainer' while going via the QQuickWindow (that doesn't know much about size policies). Maybe createWindowContainer() can be a bit smarter in how 'upwards' size hint and size policy propagation is done? (e.g. if the QQuickWindow does not have an API to specify size policy - can it can plumb together size policy of the contentItem and the returned QWidget ?)

Note that the QQuickWindow can be embedded into a layout by first wrapping the QQuickWindow with:

QWidget *hostedQuickWindow = QWidget::createWindowContainer(quickWindow);