More flexibility in BubbleBorder arrow rendering.
Currently causing the arrow not to be painted leaves a
margin of several pixels on the side the arrow would be
painted, causing issues when laying out bubbles next to an
anchor rectangle such as the edge of the screen.
This patch changes the API so that you can choose whether
the arrow is painted normally, there is space left for the
arrow but it is not painted, or there is no space left for
the arrow and it is not painted.