T-junction free regions are useful for rendering regions with various
geometric transformations, and the Region's span-ordered, sorted rect
list supports T-junction free storage without modification.
This approach creates a T-junction free region by splitting each
rectangle that is part of a vertical T-junction. This approach is two
pass (up and down) so that divisions can trickle up/down to other
adjacent spans.
Change-Id: Ifcf5e6fe0034c96b00ef09a4433b2b0fce8f4300
