Blender Git Loki

Bezier Spline: Add a more generalized insertion utility

This logic is from the curve sundivide node, used to add points with
proper handles in between two existing points. However, the same logic
is used for trimming of Bezier splines, and possibly interactive point
insertion in the future, so it's helpful as a general utility.

The logic is converted to depend on a bezier spline instead of being
static. A temporary segment spline can be used for the latter use case.