Track hover of children

Event handling of items that filter child events changed behavior a bit in Qt6. When going over a child it used to not receive an hoverLeveEvent

while now we get an hoverleave, then the filtered child will get and hoverenter, and finally the parent will get an hoverenter again, having from the user code pov, an hoverleave too much, changing behavior of the user code. In particular, this broke the mouseover for Plasma's FolderView.

This patch tracks also the hover state for filtered children, so containsmouse will always be true if either the item or a child has the mouse and doesn't emit changed signals when they are not needed