Real-time collaborative editing

[pvh]

We should support the real-time collaborative editing capabilities of Hypermerge.Text. I suspect this should be possible because there's the VSCode Live extension which seems to do something similar but we need to look into how it's implemented to learn from it.

[pvh]

We discussed approaches here and pvh prototyped something on a special (.text) key but the real-timey-ness feels weird when other fields don't have it.

Some things to figure out:

• should everything be per-character real-time editing?
• how to render Automerge.Text in general? (a big array with weird keys is not ideal)
• should we have a separate "branch" for real-time editing and merge on save to the "stable" branch? this would be neat.

[pvh]

Anyway deferred to post-CDMX