script: Remove note_rendering_opportunity and rendering_opportunity (#34575)

A rendering opportunity is now unconditionally triggered by handling IPC
messages in the `ScriptThread`, unless animations are running in which
case it's driven by the compositor. We can now remove calls to
`note_rendering_opportunity` and `rendering_opportunity`.

There is one tricky case, which is when a promise completion during a
microtask checkpoint dirties the page again. In this case we need to
trigger a new rendering opportunity, unless animations are running.  In
a followup change, when not driven by the compositor, rendering
opportunities will be driven by a timed task, meaning we can remove this
workaround.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/document.rs

@@ -2064,6 +2064,12 @@ impl Document {
         }
     }
 
+    /// Whether or not this `Document` has any active requestAnimationFrame callbacks
+    /// registered.
+    pub(crate) fn has_active_request_animation_frame_callbacks(&self) -> bool {
+        !self.animation_frame_list.borrow().is_empty()
+    }
+
     /// <https://html.spec.whatwg.org/multipage/#dom-window-requestanimationframe>
     pub(crate) fn request_animation_frame(&self, callback: AnimationFrameCallback) -> u32 {
         let ident = self.animation_frame_ident.get() + 1;