Allow Output widget in html manager to render state updates

[MrBago]

This PR adds a listener to the output widget in html-manger to update the Output Area when new outputs are added to the widget in the kernel. The PR also adds a unit test and updates the web3 example to demonstrate the change.

[github-actions]

👈 Launch a binder notebook on branch MrBago/ipywidgets/html-ow-update

[jasongrout-db]

@MrBago - thanks so much for submitting this!

**Lint / Lint (pull_request) ** Failing after 34s — Lint

We should really get a bot to run lint for us and update PRs automatically...

@MrBago - can you run yarn run lint in the repo root and commit the changes to get the lint test to pass?

[ianhi]

We should really get a bot to run lint for us and update PRs automatically...

I set up pre-commit.ci on ipympl and several other repos and find it to be quite nice. See matplotlib/ipympl#362

[jasongrout]

Thanks @MrBago. This looks great. The image zoom was mesmerizing.

For those who have always wondered, this is what a Jupyter Logo looks like at 1x1 pixels on a hidpi screen (magnified by a factor of 4 to see it easier):

[jasongrout]

@meeseeksdev please backport to 7.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 7.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -m1 209452610c4e5dc6ec4d52b71cb2172e4ba7e03d

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #3370: Allow Output widget in html manager to render state updates'

4. Push to a named branch:

git push YOURFORK 7.x:auto-backport-of-pr-3370-on-7.x

5. Create a PR against branch 7.x, I would have named this PR:

"Backport PR #3370 on branch 7.x (Allow Output widget in html manager to render state updates)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.