Issues addressed: - exception when trimming a loose end of a Arc of circle - conflicting constraints when trimming - loss of tangency when trimming arcs tangent to lines or other curves - incorrect trimming when the intersecing geometry has a PointOnObject constraint to the arc, but also another intersection og geometry. Fixes: https://tracker.freecadweb.org/view.php?id=4066 https://tracker.freecadweb.org/view.php?id=3910 Also see forum discussion https://forum.freecadweb.org/viewtopic.php?f=10&t=53299