This removes a whole lot of code from `pathfinder_path_utils`. Hopefully
the remaining code can go upstream.
These changes regress quality of stroke widths for cubic curves, because
they move fill-to-stroke conversion before cubic-to-quadratic
conversion. To fix that, we will need to recursively subdivide when
doing fill-to-stroke conversion.
These extra points are unnecessary and can confuse the partitioner,
because they sometimes prevent it from detecting winding numbers
properly. This is a bug in the partitioner and should be fixed, but we
shouldn't be generating these points to begin with.
Partially addresses #57.
I'm not too happy with this, as I discovered a segfault in FreeType that doesn't give me confidence
in this as a solution for the long term. Additionally, this exposes the problems in the partitioner
with lack of winding fill rule, proper handling of self-intersections, and splitting of paths at
their extrema. (I believe these problems should be fairly straightforward to handle, but we just
don't handle them yet.)