Summary:
The previous approach of setting some of the borders to be thicker and different colours was flakey, sometimes parts of the border would be cut off by a parent
With this approach we figure out the offset relative to the root of the visualiser, and draw a box that is definatley on top. It works much more reliably
Also fixed a couple of other niggles:
1. Can unselect when clicking again
2. Going into focus mode clears selection since your selection may not be in the focused area and there is a phantom box
Reviewed By: lblasa
Differential Revision: D46224034
fbshipit-source-id: 24bed8db38cddab796f786e7e0a4acfe7c6a9089
c13180a929