Calculations in Adaptor2d_OffsetCurve are unified with similar calculations in Geom2d_OffsetCurve using methods extracted from Geom2dEvaluator_OffsetCurve to Geom2dEvaluator.cxx
BRepFill_OffsetWire.cxx, Geom2dGcc_Circ2d2TanRadGeo.cxx, Geom2dGcc_Circ2dTanOnRadGeo.cxx, MAT2d_Circuit.cxx are modified to satisfy changing offset direction.
