Previous commit mistakenly included the full clearance for the rounded
rectangle circle. The CFILLEDCIRCLE2d takes the radius rather than the
diameter.
Apply same logic of using a filled circle to represent a zero-length
element as a filled circle with radius of the line.
Fixes: lp:1785823
* https://bugs.launchpad.net/kicad/+bug/1785823
Replaces Poly2Tri with updated code to process polygons faster and more
robustly. Notably, we can now handle overlapping holes in the polygons,
allowing us to cache the triangulation of complex boards