Allow removing event listeners by group

[domenic]

Closes #208.

Tests: web-platform-tests/wpt#6331

Chrome is tentatively interested in this, although the first step is getting a spec and tests up for review. Would love to hear if other implementers are interested--- @smaug----, @cdumez, @travisleithead?

I decided to go with an overload instead of a new method, so we can leave new method names for something potentially nicer like on/off. Overloading for this pattern is pretty common, e.g. it is what jQuery does. And introducing two similar-but-different method names like removeEventListener + deleteEventListener seemed like a bad idea.

I also added an overload removeEventListener(type, { group }) which is not really necessary. We could get rid of that if we don't like it. But it fell out naturally.

This also preserves what I'm pretty sure is a bug, per #468, but at least it centralizes the probably-buggy check.

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Preview | Diff

[smaug----]

( This is a pull request so try to not comment API proposal here. )

[Krinkle]

cookies is a fun and lightweight example word, but I think in this context it has the risk of confusing less-experienced readers due to being an overloaded term. Perhaps we can come up with another example here, or if nothing else, plain "example".

[domenic]

Thanks. Will make it brownies instead during the next revision.

[kenchris]

I was wondering whether supplying a signal like the AbortController/AbortSignal would make more sense instead of groups. Then you can abort multiple things with the same controller.

const controller = new AbortController();
accelerometer.addEventListener('reading', listener, {signal:controller.signal});
controller.abort();

[annevk]

I suggest we close this now that you can use abort signals as grouping mechanism thanks to @benjamingr's work. Thoughts?

[domenic]

Oh, right, this was mine originally. Yeah, signals is basically a better version of this; let's close!