It is enough to just set the parent (and make the parent
call gtk_native_check_resize in size_allocate).
This commit removes the relative_to argument to the
constructors of GtkPopover and GtkPopoverMenu, and
updates all callers.
Menus traditionally don't have separate
hover and focus locations. Make the same
change here that we already did for
popover menubars: Track the active item
and set its selected state. Both keynav
and mouse change the active item.
