Optimize Bézier bisections. * src/raster/ftraster.c (Split_Conic, Split_Cubic): Use shifts and refactor. * src/smooth/ftgrays.c (gray_split_conic, gray_split_cubic): Ditto. * src/base/ftstroke.c (ft_conic_split, ft_cubic_split): Ditto. * src/base/ftbbox.c (cubic_peak): Use shifts.