UX: Avoid dialog box to say "Directory not found"

[consideRatio]

I'm often removing a folder from terminal that I'm browsing in the view to he left, and after some seconds of delay I end up with a dialog box that I need to dismiss before continuing to do work in the terminal. I'm not sure what to do instead, but similar to many applications decides to show "connection lost" as a status bar or similar rather than a dialog popup, I think it would be suitable to show the "Directory not found" not as a modal dialog, but as some status within the content manager to the left.

GIF animation of the UX in Jupyter Lab 0.35.6

[krassowski]

This is reproducible in 1.0.2. An alternative to the proposed solution would be to use a toast notification (see #6389) once merged instead of the modal; the toast might be better as it is still exposed to the user and thus might minimize confusion in a scenario when the directory was removed (or moved) by another process (i.e. not intentionally by the user as shown above).

[consideRatio]

A good improvement from whats seen here in Jupyter Lab 1.0.1 is that the content manager leaves the folder, so the dialog box will only show once.