[Sketcher] Refactor SketchObject::trim()

DO NOT MERGE because not complete: not all constraints are not transferred.

Includes:

* Adjust `deriveConstraintsForPieces` for trim
* Make sure new points are constrained on the cutting edges
* Add constraints at trim end(s) dependent on pre-exisiting ones with cutting curve(s). Also change tests to reflect that auto-coincidence can now be applied to non-periodic curves as well.

Known issue(s):
* Some redundant constraints may be added under certain circumstances (e.g. in
presence of perpendicular-via-point)

src/Mod/Sketcher/App/SketchObject.h

@@ -410,7 +410,8 @@ public:
     /// the constraint that will replace the given one (which is to be deleted). NOTE: Currently
     /// assuming all constraints on the end points of the old curve have been transferred or
     /// destroyed
-    void deriveConstraintsForPieces(const int oldId,
+    /// Returns whether or not new constraint(s) was/were added.
+    bool deriveConstraintsForPieces(const int oldId,
                                     const std::vector<int> newIds,
                                     const Constraint* con,
                                     std::vector<Constraint*>& newConstraints);
@@ -455,6 +456,7 @@ public:
                 double perpscale = 1.0);
 
     int removeAxesAlignment(const std::vector<int>& geoIdList);
+    static bool isClosedCurve(const Part::Geometry* geo);
     static bool hasInternalGeometry(const Part::Geometry* geo);
     /// Exposes all internal geometry of an object supporting internal geometry
     /*!