Surface: ViewProviderExtend for Surface::Extend object

This is created by the Surface_ExtendFace command.

src/Mod/Surface/App/FeatureExtend.h

@@ -53,6 +53,10 @@ public:
     // recalculate the feature
     App::DocumentObjectExecReturn *execute(void) override;
     short mustExecute() const override;
+    /// returns the type name of the view provider
+    const char* getViewProviderName(void) const override {
+        return "SurfaceGui::ViewProviderExtend";
+    }
 
 protected:
     virtual void onChanged(const App::Property* prop) override;