Use monotonic time instead of 0 for motion events

Update to https://github.com/Smithay/smithay/pull/1509, and adopt a
similar change.

src/wayland/handlers/toplevel_management.rs

@@ -73,7 +73,7 @@ impl ToplevelManagementHandler for State {
                                     &MotionEvent {
                                         location: new_pos.to_f64().as_logical(),
                                         serial,
-                                        time: 0,
+                                        time: self.common.clock.now().as_millis(),
                                     },
                                 );
                                 ptr.frame(self);