fix: use document GUID as prosemirror reference to avoid updating deleted documents

[bosschaert]

Description

Previously the prosemirror document would be stored in the 'prosemirror' attribute
on the YDoc. This changes that to be prosemirror-${guid}.
This is to avoid accidentally left open editors from accidentally re-creating a deleted document.

Required this change on the editor side: adobe/da-live#564

Related Issue

da-collab part of the fix for adobe/da-live#378

How Has This Been Tested?

• New Unit test
• Extended Playwright test

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[github-actions]

LCOV of commit c97cab8 during Install, lint, and test #210

Summary coverage rate:
  lines......: 95.5% (1735 of 1817 lines)
  functions..: 96.7% (59 of 61 functions)
  branches...: no data found

Files changed coverage rate:
                  |Lines       |Functions  |Branches    
  Filename        |Rate     Num|Rate    Num|Rate     Num
  ======================================================
  src/collab.js   | 3.7%    434| 0.0%    16|    -      0
  src/edge.js     | 2.7%    331| 0.0%     8|    -      0
  src/shareddoc.js| 3.1%    675| 0.0%    21|    -      0