Be able to use Shift+Alt+Up/Down/Left/Right to move to another monitor even if _NET_WM_FULLSCREEN_MONITORS is set.
Feature summary
For example, when _NET_WM_FULLSCREEN_MONITORS is set to (0,0,0,0), Mutter adds a fullscreen constraint so that a window with the property cannot be moved to another monitor. The constraint flag is from the META_MOVE_RESIZE_CONSTRAIN from the meta_window_move_resize_internal() call in meta_window_move_between_rects(), which is called by meta_window_move_to_monitor().
How would you like it to work
Allow the window to be moved even if the property is set since it's a user action. Other window managers such as KWin allow this. I know this is not part of the wm-spec. I created this issue to invite discussion about whether we should change this behavior before writing any code.