Should `StableSocket` just extend `EventTarget`

It's a little un-idiomatic to use delegate objects as a "callback bag" in the Web Platform.

This could potentially, instead, use EventTarget, and emit events for each of the callbacks we have in the `delegate` object. This gives us a lot more flexibility with handling these lifecycle steps.

Start by reading the StableSocket implementation and the delegate callbacks described in the issue. Determine whether extending EventTarget can replace the callback-bag design while preserving the existing lifecycle behavior; the issue is done when that design decision and its required scope are clear.

Written by the indexing model from the issue text.