This commit implements generic evaluation for Bezier curves (which is really just linear interpolation, since attributes are not stored on Bezier handles). For complete parity with the old curve type, we would have to add options for this (RNA: `Spline.radius_interpolation`), but it's not clear that we want to do that. This also adds a generic `interpolate_to_evaluate` utility on curves that hides the implementation details. Though there is theoretically a performance cost to that, without some abstraction calling code would usually be too complex. Differential Revision: https://developer.blender.org/D14447