R1:61318a8119d3

Improve minor workboard drag behaviors

Summary:
Ref T5240.

- Add proper class when dropping cards.
- Add proper class when creating new cards.
- Make X-drag explicit so that it works if there's only one column.
- Stop tootips when dragging, resume them after dropping.
- Move CSS rule for consistency.
- Allow user to hit "Escape" to cancel an in-progress drag.

Test Plan:
- Dropped cards.
- Created new cards.
- X-dragged on a workboard with one column and a dashboard.
- Dragged over a…