Emitted when the state of window changes.
This can happen when window is (un)minimized, (un)maximized, (un)sticked, (un)shaded, (un)made above, (un)made below,
(un)set fullscreen, when it needs attention, etc. See WindowState for the complete list
of states that might have changed.
| changed_mask |
the bitmask containing bits set for all states of |
| new_state |
the new state of |