This commit ports the "Set Handle Positions" and "Set Hanle Type" nodes to use the new curves data-block. The nodes become simpler and likely much faster too, though they're usually not the bottleneck anyway. Most of the code is ported from `BezierSpline` directly. The majority of the complexity comes from the interaction between different automatically calculated handle types. In comparison `BezierSpline`, the calculation of auto handles is done eagerly-- mostly because it's simpler. Eventually lazy calculation might be good to add. Differential Revision: https://developer.blender.org/D14464