Update content of unchanged file when changed on the server

Follow up to #4078

Is your feature request related to a problem? Please describe.
When reverting to a previous version or changing the content of a file on the server via another means we currently make the editor read only and display

Instead it would be nice to load the new content and keep the editor editable.

Describe the solution you'd like

We already detect that the editing session was cleared. Reload the editor fetching the new file and creating a new editing session.

Describe alternatives you've considered

Automatically reloading the entire page feels too intrusive.
Better wording of the error message would be a start but still leaves the user with one option we expect them to click.

Additional context

We might want to still show a message indicating that the content updated - but we would also not do that if the content was updated inside another text editor session. So I think it would be

Start by tracing the existing handling for a cleared editing session and how the editor currently becomes read-only when server content changes. Verify how a fresh file fetch and editing session are initiated, then confirm that the editor remains editable with the server's new content without reloading the page.