libservo: Allow embedders to signal when the cursor has left the WebView (#37317)

Currently, the hover state will stay when the mouse moves out of the
webview, this PR fixes it

Testing: Hover on the `About` on servo.org, and then move the mouse up
to the browser UI, see the hover state resets

Signed-off-by: Tony <legendmastertony@gmail.com>

components/script/dom/document.rs

@@ -2113,6 +2113,49 @@ impl Document {
         }
     }
 
+    #[allow(unsafe_code)]
+    pub(crate) fn handle_mouse_leave_event(
+        &self,
+        hit_test_result: Option<CompositorHitTestResult>,
+        pressed_mouse_buttons: u16,
+        can_gc: CanGc,
+    ) {
+        // Ignore all incoming events without a hit test.
+        let Some(hit_test_result) = hit_test_result else {
+            return;
+        };
+
+        self.window()
+            .send_to_embedder(EmbedderMsg::Status(self.webview_id(), None));
+
+        let node = unsafe { node::from_untrusted_node_address(hit_test_result.node) };
+        for element in node
+            .inclusive_ancestors(ShadowIncluding::No)
+            .filter_map(DomRoot::downcast::<Element>)
+        {
+            element.set_hover_state(false);
+            element.set_active_state(false);
+        }
+
+        self.fire_mouse_event(
+            hit_test_result.point_in_viewport,
+            node.upcast(),
+            FireMouseEventType::Out,
+            EventBubbles::Bubbles,
+            EventCancelable::Cancelable,
+            pressed_mouse_buttons,
+            can_gc,
+        );
+        self.handle_mouse_enter_leave_event(
+            hit_test_result.point_in_viewport,
+            FireMouseEventType::Leave,
+            None,
+            node,
+            pressed_mouse_buttons,
+            can_gc,
+        );
+    }
+
     fn handle_mouse_enter_leave_event(
         &self,
         client_point: Point2D<f32>,

components/script/script_thread.rs

@@ -1127,6 +1127,14 @@ impl ScriptThread {
                         can_gc,
                     );
                 },
+                InputEvent::MouseLeave(_) => {
+                    self.topmost_mouse_over_target.take();
+                    document.handle_mouse_leave_event(
+                        event.hit_test_result,
+                        event.pressed_mouse_buttons,
+                        can_gc,
+                    );
+                },
                 InputEvent::Touch(touch_event) => {
                     let touch_result =
                         document.handle_touch_event(touch_event, event.hit_test_result, can_gc);