fix: prevent other (e.g. website, extensions) scripts from receiving 'ratechange' event when switching to silenceSpeed?

[WofWca]

You may say that It's kind of a non-normal thing that we switch to such high playback rate so maybe we shouldn't let other scripts notice that it's happening. Websites may watch 'ratechange' event and, for example, update user's website settings (playback rate), or something else.

Note that this is not the same as

jumpcutter/src/entry-points/content/AllMediaElementsController.ts

Lines 584 to 599 in c63821f

	case 'prevent': {
	// Consider doing this for `defaultPlaybackRate` as well.
	const lastPlaybackRateSetByUs = lastPlaybackRateSetByThisExtensionMap.get(el_);
	if (
	el_.playbackRate !== lastPlaybackRateSetByUs
	// Just in case.
	&& lastPlaybackRateSetByUs !== undefined
	) {
	setPlaybackRateAndRememberIt(el_, lastPlaybackRateSetByUs);
	// The website may be listening to 'ratechange' events and update `playbackRate`
	// inside the listener. Let's make it so that it doesn't receive the event.
	// This happens on Twitch (https://github.com/WofWca/jumpcutter/issues/25).
	event.stopImmediatePropagation();
	}
	break;
	}

because there we .stopImmediatePropagation() for all ratechange events, not just for silenceSpeed.

It may help with compatibility with other playbackRate controlling extensions like "Video Speed Controller".

Not sure if we need this, need to know practical cases (besides maybe #25). Maybe make a per-site setting for this, idk.

To do this, look at event.stopPropagation( / event.stopImmediatePropagation( and related stuff.

Related #25