Auto merge of #22348 - germangb:html_media_ended, r=ferjm

Implement Ended media attribute

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This PR should implement:
* New method `HTMLMediaElement::earliest_possible_position()` for the [earliest possible position](https://html.spec.whatwg.org/multipage/media.html#earliest-possible-position)
* `Ended` attribute following https://html.spec.whatwg.org/multipage/media.html#ended-playback
* Queue steps for when the playback position reaches the end

This PR contains placeholders for the following issues (I can rebase changes after the corresponding PRs get merged)
- #22321 (Define the Loop attribute)
- #22293 (To identify playback direction. Either forwards or backwards)

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [x] These changes fix #22294.

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components/script/dom/webidls/HTMLMediaElement.webidl

@@ -46,7 +46,7 @@ interface HTMLMediaElement : HTMLElement {
   [Throws] attribute double playbackRate;
   readonly attribute TimeRanges played;
   // readonly attribute TimeRanges seekable;
-  // readonly attribute boolean ended;
+  readonly attribute boolean ended;
   [CEReactions] attribute boolean autoplay;
   // [CEReactions] attribute boolean loop;
   Promise<void> play();