onBeforeElUpdated for events clobber's user's provided version

This was already addressed here originally in PR #44 . but then taken out to simplify that PR. To paraphrase:

We use our own custom onBeforeElUpdated function for memoizing sub-components, but then lose the ability to copy events. We'd need to be able to use both, ideally running the user function before the copier (since the user returning false immediately would make the event copier operations redundant).

I've seen the memoization example from the "choo stateful playground" example (though we aren't using choo directly), but it would be better at least for our purposes to have the isSameNode check internalized once in our main node comparison, rather than needing to include customElement.isSameNode = () => true; comparisons externally at the root of every one of our memoized sub-components (though only after the first update, which again adds more closure boilerplate if the same component is being used multiple times).

If there would be a way to get in @kristoferjoseph s work via this issue that would be great :)

Start by reviewing the implementation of onBeforeElUpdated and the changes discussed in PR #44. Trace how the custom memoization callback interacts with event copying and isSameNode; done means user callbacks and event copying can coexist with the intended callback ordering and memoization behavior.