No way to listen to errors dispatched during initialization.

[theengineear]

Currently, our pattern is to call .dispatchError such that some integrator can do .addEventListener('error', () => { /* .. */ }) and listen to errors from children. However, errors can happen during connection.

We need to do something different here since we're missing signals about errors which can cause silent failures.

[theengineear]

@klebba ran into this one recently and did a lot of head-scratching before I realized what was going on. I think there are two options:

1. defer more initialization until first connectedCallback
2. fork logic and console.error when not connected (hate this idea, we're not doing this)
3. hard-throw errors during initialization (also dislike this...)

I'm sort of leaning towards (1). We can still do everything synchronously, but we just do a little less during construction, preferring to wait until connectedCallback.

In particular, any reservations to deferring property analysis until first connected callback?

[theengineear]

^^ I went ahead and made this change locally. It's much, much better. One side effect here is that we can see previously-hidden setup errors in demos again 🥇. Additionally, it's possible to test for these errors in /test 🥈.