030e6aa507
Previously, the overview BoxLayout was sized and positioned explicitly using the primary monitor coordinates, as its parent was at 0,0 and with a fixed layout manager. Now we use a bin layout, so we need to position and size the stack actor, and set the overview boxlayout to expand. Take also the occasion to use a MonitorConstraint instead of handling position and size manually. https://bugzilla.gnome.org/show_bug.cgi?id=694969