User:HooglyBoogly/GSoC2019/ProfileWidget Fill

The Original Method
The fill has to be more complicated because the profile can loop back on itself in the X direction. The fill can't just be a simple inequality anymore. Here's the new strategy:

For every horizontal pixel, do the following:
 * 1) Find all of the edges between `ProfilePoints` in the profile's `table` that will have the same Y value as this pixel.
 * 2) Sort those edges by their intersection point with the current pixel's X value (the Y value at this X)
 * 3) Go through the list, switching between drawing a light and dark edge to the next intersection point after each edge. Start with light.

This could be sped up by making a list in the profile table sorted by their X values. That way the first step would only have to be done once at the beginning of the whole process.

The Triangulation Method
I started to implement the profile color fill algorithm I described above, but I've been dissapointed by how inefficient it seems, and I'm pretty sure I thought of a better solution. I'm hoping to be able to use an existing triangulation algorithm in `polyfill_2d.c` to fill the "polygon" of the custom profile with a darker color. My original method would have been O(x_width * nlogn) (where n is the number of points in the table), and it looks like a triangulation algorithm would at least drop that x_width term, which could be very helpful. The only new issue this brings up is the translation from the `ProfilePoints` to the triangulation code, and then from the triangulation code to primitive triangles drawn by the GPU in the interface. If there isn't too much overhead in these transitions, this technique will probably work a lot better.