TD: fix memory leaks with raw pointers of GeometryObject

Replacing the use of raw pointers of GeometryObject with shared pointers fixes the observed memory leaks when running the unit tests of TechDraw

src/Mod/TechDraw/App/GeometryObject.h

@@ -25,6 +25,7 @@
 
 #include <Mod/TechDraw/TechDrawGlobal.h>
 
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -222,6 +223,8 @@ protected:
     bool m_usePolygonHLR;
 };
 
+using GeometryObjectPtr = std::shared_ptr<GeometryObject>;
+
 } //namespace TechDraw
 
 #endif