script: Expose NodeTraits::owner_global / Window::as_global_scope (#34843)

Expose two new helpers and start using them as much as possible.

- `NodeTraits::owner_global`: which gets the `GlobalScope` that currenty
 owns a `Node`. This may be different than `.global()` in the case that
 the `Node` was adopted by a different `Document`.
- `Window::as_global_scope`: A helper to avoid having to cast so much
  when treating a `Window` like a `GlobalScope`.

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

components/script/dom/htmlstyleelement.rs

@@ -133,7 +133,7 @@ impl HTMLStyleElement {
 
         // No subresource loads were triggered, queue load event
         if self.pending_loads.get() == 0 {
-            self.owner_window()
+            self.owner_global()
                 .task_manager()
                 .dom_manipulation_task_source()
                 .queue_simple_event(self.upcast(), atom!("load"));