Convert surface normal to return by value, no need for allocation. Tidy up Boundary Surface implementations

Convert surface normal to return by value, no need for allocation. Tidy up Boundary Surface implementations

Mentioning @sroe

Tracking/TrkDetDescr/TrkSurfaces/TrkSurfaces/ConeSurface.h

@@ -184,8 +184,7 @@ public:
 
   /**Return method for surface normal information
      at a given local point, overwrites the normal() from base class.*/
-  Amg::Vector3D normal(
-    const Amg::Vector2D& locpo) const;
+  virtual Amg::Vector3D normal(const Amg::Vector2D& locpo) const override final;
 
   /**Return method for the rotational symmetry axis - the z-Axis of the
    * HepTransform */