Sketcher: New Feature: Symmetric tool

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Creates geometry symmetric to the selected one with respect to the last selected point or line.

It does not support the following constraints:

- Angle
- Horiz/vertical distance
- SnellLaw

Horizontal and Vertical (directional) dimensions removed from the the copying process when created
on a single edge (by picking one edge instead of two points), i.e. Constraint involving only one GeoId at "First".

src/Mod/Sketcher/App/SketchObject.h

@@ -150,6 +150,8 @@ public:
 
     /// trim a curve
     int trim(int geoId, const Base::Vector3d& point);
+    /// adds symmetric geometric elements with respect to the refGeoId (line or point)
+    int addSymmetric(const std::vector<int> &geoIdList, int refGeoId, Sketcher::PointPos refPosId=Sketcher::none);
     /// Exposes all internal geometry of an object supporting internal geometry
     /*!
      * \return -1 on error