A way out is the user finishing the interaction, which is more than the mode ending: an edit also
ends when Enter moves on to the next cell. A feature that follows the user rather than the mode (the
virtual keyboard going down) listens here, so the chrome needs no knowledge of it.
Take a way out of a mode from chrome (the status bar's ✓ / ✕): tells the subscribeEditModeExit listeners, then runs the mode's own
doneorcancel.