Constraint data is represented as below. Generally, constraints are defined by a target face ("from_face") and a reference ("to_object").
Target Face is one of the faces defined by UF_MODL_dfo_region_t. Constraint reference can be face, edge, line, datum plane, datum axis, etc.,
and and it is always abstracted as a direction and a point, thus the input 'to_object' should be a smart direction based
on an underlying entity (see uf_so.h). Some constraint types, such as angle, parallel, perpendicular and tangent, will
need a smart point to control the result, namely, "thru_point", which specifies that the destination of the target face
will pass through some point.