Sketcher: Fix several issues in SketchObject::trim
Sketcher: Fix several issues in SketchObject::trim

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

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