SYSML21 — ShapeItems can't be SpatialItems

[From Dr. Charles Manion] SpatialItem (eventually) specializes KerML Body, which are required to be 3 dimensional (innerSpaceDimension=3), but the "shapes" in ShapeItems.sysml are all lower dimensional (Curves and Surfaces, innerSpaceDimension=1 and 2, respectively). Since SpatialItem defines coordinates, it would be contradictory to give shapes (and Points, innerSpaceDimension= 0) coordinates.