Undo/redo and other shortcuts cause issues with in progress keyboard move

[microbit-matt-hillsdon]

Most actions disable themselves during a mouse drag but they don't during a keyboard move.

This causes mayhem, especially with undo/redo.

Unexpected state following move + clean-up:

Unexpected state following move + undo and subsequent arrow movement:

[rachel-fenichel]

Undo and redo are implemented in core's shortcut_items.ts and preconditions that check Gesture.inProgress.

inProgress checks the workspace's currentGesture directly instead of calling getGesture, so this won't be fixed by #400.

Short-term solution: copy in undo/redo and check workspace.isDragging() in the precondition.

Solution for other shortcuts: Add a check of workspace.isDragging() to navigation.canCurrentlyEdit and/or navigation.canCurrentlyNavigate.

Long-term solution: include checks for keyboard drags in workspace.isDragging() implementation in core.