Share updates to submission across tabs

[matthew-white]

Right now, the following sequence is possible:

• Navigate to the submissions table.
• Open an individual submission in a new tab by clicking the More button.
• In the new tab, make a change to the submission.
• Return to the first tab. The submissions table does not reflect the change made in the new tab.

There are a couple of different updates that could happen in the new tab:

1. The submission's review state is updated.
2. The submission is edited (that is, a new version of the submission is created).

We can definitely hook into (1). For (2), is Frontend able to detect when the user completes an edit in Enketo? (In that case, Enketo redirects to Frontend. We can probably check for that, right?)

I'm thinking that this may be a good use case for BroadcastChannel, which is at last supported in Safari. getodk/central-frontend#706 is another issue for which we might use BroadcastChannel.

[matthew-white]

Should we also do something similar for updates to entities (including resolving a conflict)?