Fix submenu positioning

Fix submenu positioning

Submenus are now positioned to the correct side of the parent menu
based on layout direction, if there is enough space on screen to fit
the menu. If there is insufficient space, then the menu is positioned
to the other side of the parent menu. In case that also causes submenu
to be partially ofscreen (very wide menu relative to the screen),
then the submenu will be aligned with the screen edge and will overlap
the parent menu. This seems like a lesser evil compared to having
submenu partially offscreen, which could obscure important details
such as checkmarks.

Task-number: QTBUG-23568
Change-Id: I6a9ab2c232713a2ee5a6dde3227c40419d46bd3d
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>