Role: This API creates an edge whose underlying geometry is a spline
curve (that is, an intcurve) using the geometry underlying the given edge. It first
creates an intcurve from the geometry of the given edge. It then uses the new
intcurve to create a new spline edge. The direction of the new edge is the same
as given edge. If the argument for the new spline edge is a NULL reference, the
existing edge is converted to a spline edge.