Prevent loss of layout changes when discarding changes in a different workspace or Live

Problem/Motivation

Layout builder locks are not workspace-safe: by breaking them in Live you may delete unsaved layout changes performed inside a workspace.

Steps to reproduce

1. Log in as admin
2. Enable layout builder on the article content type and allow per-node customization
3. Create a new article in Live
4. Create a workspace Test
5. Edit the article above's layout and swap a couple of blocks without saving
6. Create an admin-2 user and log in
7. Switch to Live
8. Visit the article layout page
9. Discard the changes
10. Log back in as admin user and switch back to the Test workspace
11. Visit the article layout page
12. Observe

Proposed resolution

Introduce a workspace aware shared tempstore in the workspaces module.