A normalized vector that points from pointB to pointA.
The normalized vector points from ColliderDistance2D.pointB to ColliderDistance2D.pointA. When it is scaled with the ColliderDistance2D.distance is produces a vector that can be used to move the Collider2D so that they are no longer overlapped (if the ColliderDistance2D.distance is negative) or so they are touching (if the ColliderDistance2D.distance is positive).