Add an indicator for chat sessions with unkept file changes

When multiple Chat sessions make file edits, it is difficult to determine which sessions still contain changes that have not been accepted with Keep.

Please add a visible indicator or filter in the Chat session history showing sessions with pending edits. Ideally, users should be able to:

- Identify sessions with unkept changes at a glance.
- Filter or sort sessions by pending changes.
- See which files have pending changes.
- Resume a session and review, keep, or discard those changes.

FTR, I am using vscode 1.138.0 with copilot chat v0.66.0.

Prior to a few releases ago, I could look at the session list and any session with the green/red change counts would indicate changes that had not been kept, but now all sessions show this, whether there are pending changes or not.