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
00ba51d37b