Monkeypatch `WorkspaceSvg.isDragging` to return true if a keyboard "drag" is in progress

[rachel-fenichel]

Current implementation:

  /**
   * Is the user currently dragging a block or scrolling the flyout/workspace?
   *
   * @returns True if currently dragging or scrolling.
   */
  isDragging(): boolean {
    return this.currentGesture_ !== null && this.currentGesture_.isDragging();
  }

This is causing issues with testing the constrained and unconstrained dragging because an interaction with the disableOrphans listener makes the moving block appear disabled.

Proposed solution

In DragMover.startMove, monkeypatch isDragging to return true.
In DragMover.finishMove and DragMover.abortMove, undo the monkeypatch and restore the normal function.

Additional information

Longer term, we'll need the workspace to know whether a keyboard drag is in progress, because the keyboard drags won't be registered as gestures.