Collaborative Editing iteration for WordPress 7.0

[maxschmeling]

This issue serves as the iteration / tracking issue for Collaborative Editing functionality planned for WordPress 7.0.

We're focusing primarily on the Gutenberg post editing experience for WordPress 7.0 collaborative editing functionality. Multiple editors should be able to open posts they have access to without seeing a post lock dialog, understand who else is editing the post and which part of the post they are editing, and then save their combined changes to the database in the same way a revision is saved today.

The work for WordPress 7.0 does not include suggested edits, user controllable editing modes, or live mouse positions (as suggested in the design doc).

The work on RTC has been organized into three layers:

• Interface: User-facing elements, avatars, presence indicators, revised lock messaging.
• Engine: The Yjs-based technology that records and merges changes in real-time.
• Transport: Services that synchronize data between collaborators.

Each sub-issue will have a prefix in the title with which of these layers it involves to aid in navigating the work being done.

Designs

The designs below are early explorations. @DavidBowman is working on updating them to match our WP 7.0 target.