Add function to compute area of region bounded by c2c contours

[kennyweiss]

It would be useful to compute the area of the region bounded by a closed set of contours.
For example, this can be used to measure the accuracy of our shaping algorithms.

Since we currently load c2c contours as NURBS curves, we can apply Bezier extraction on each curve (i.e. extract a rational Bezier curve for each knot span) to create a primal::CurvedPolygon for the regions. We already have the ability to compute the area of a closed primal::CurvedPolygon.