This commit removes the use of PolySpline for resampling curves and
replaces it with the length parameterization utility for that purpose.
I didn't test performance, but I would expect the shrinking to be
slightly faster because I reused some arrays to avoid allocating
them for every curve. I noted some potential improvements in
the "add curves" function.
Differential Revision: https://developer.blender.org/D15342
215f805ce6