compositor: Make input event handling per-WebView (#35716)

This is another step in the move to having a per-WebView renderer. In
this step event handling is made per-WebView. Most events sent to Servo
are sent via the WebView API already, so this just moves more event
handling code to the per-WebView render portion of the compositor.

- ServoRenderer is given shared ownership and interior mutability as
  it is now shared among all WebView(Renderers).
- Some messages coming from other parts of Servo must now carry a
  WebViewId as well so that they can be associated with a particular
  WebView.
- There needs to be some reorganization of `ServoRenderer` in order to
  avoid issues with double borrow of `RefCells`.

Signed-off-by: Delan Azabani <dazabani@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/servo/webview.rs

@@ -339,23 +339,30 @@ impl WebView {
         point: DeviceIntPoint,
         touch_event_action: TouchEventType,
     ) {
-        self.inner()
-            .compositor
-            .borrow_mut()
-            .on_scroll_event(location, point, touch_event_action);
+        self.inner().compositor.borrow_mut().notify_scroll_event(
+            self.id(),
+            location,
+            point,
+            touch_event_action,
+        );
     }
 
     pub fn notify_input_event(&self, event: InputEvent) {
         // Events with a `point` first go to the compositor for hit testing.
         if event.point().is_some() {
-            self.inner().compositor.borrow_mut().on_input_event(event);
+            self.inner()
+                .compositor
+                .borrow_mut()
+                .notify_input_event(self.id(), event);
             return;
         }
 
         self.inner()
             .constellation_proxy
             .send(ConstellationMsg::ForwardInputEvent(
-                event, None, /* hit_test */
+                self.id(),
+                event,
+                None, /* hit_test */
             ))
     }
 
@@ -366,7 +373,7 @@ impl WebView {
     }
 
     pub fn notify_vsync(&self) {
-        self.inner().compositor.borrow_mut().on_vsync();
+        self.inner().compositor.borrow_mut().on_vsync(self.id());
     }
 
     pub fn resize(&self, new_size: PhysicalSize<u32>) {
@@ -401,7 +408,7 @@ impl WebView {
         self.inner()
             .compositor
             .borrow_mut()
-            .on_pinch_zoom_window_event(new_pinch_zoom);
+            .set_pinch_zoom(self.id(), new_pinch_zoom);
     }
 
     pub fn exit_fullscreen(&self) {