Make *ItemBoundingRect modes work with custom shapes.

Currently, calling
QGraphicsScene::items(QPointF(0, 0), Qt::IntersectsItemBoundingRect) or
QGraphicsScene::items(QPointF(0, 0), Qt::ContainsItemBoundingRect)
will exclude items whose shape does not contain QPointF(0, 0). This is
because QGraphicsSceneIndexPointIntersector::intersect() also checks if
the point is contained within the shape, instead of just checking
if it is contained within the bounding rect.

Task-number: QTBUG-19036

Change-Id: Ie701af2a5694d40cf9b3c9c19adbb09a53a4e398
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Andreas Aardal Hanssen <andreas@hanssen.name>