Existing method was fine for basic polygons but didn't scale well
because its was checking all coordinates for every y-pixel.
Heres an optimized version.
Basic logic remains the same this just maintains an ordered list of intersections,
tracking in-out points, to avoid re-computing every row,
this means sorting is only done once when out of order segments are found,
the segments only need to be re-ordered if they cross each other.
Speedup isn't linear, test with full-screen complex lasso gave 11x speedup.
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