Be able to set boundaries for the items of a graphicsview

QGraphicsItems can be moved by the user anywhere in an QGraphicsScene. Is is often useful to limit the area where the items can be (e.g. in the sceneRect, in the parent rect, etc).

For those use cases, it would be nice to have a method like QGraphicsItem::setPositionBoundingRect(const QRectF &posBoundingRect) to define the area (in parent coordinate) where the QGraphicsItem::boudingRect() is contained.