script: Consolidate step 22 of per-Document rendering update (#37703)

The parts of step 22 were a bit scattered throughout the codebase, so
this
change moves them all to a single method which does three things:

1. Update all animating images
2. Flush all dirty canvases (2D, WebGL, and WebGPU)
3. Calls reflow on the `Document`

Testing: This shouldn't change behavior in any major way so it should
be covered by existing WPT tests.

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

components/script/dom/window.rs

@@ -2173,17 +2173,8 @@ impl Window {
         let document = self.Document();
 
         let stylesheets_changed = document.flush_stylesheets_for_reflow();
-
-        // If this reflow is for display, ensure webgl canvases are composited with
-        // up-to-date contents.
         let for_display = reflow_goal.needs_display();
-        if for_display {
-            document.flush_dirty_webgl_canvases();
-            document.flush_dirty_2d_canvases();
-        }
-
         let pending_restyles = document.drain_pending_restyles();
-
         let dirty_root = document
             .take_dirty_root()
             .filter(|_| !stylesheets_changed)