Mark internal class as `final`

The internal `Element` class implements the pure virtual interface
`IElement` which has no virtual destructor. `Element` has data members
but is deleted through an `Element*` so all members are destructed
correctly.
To convince the compiler this is all fine and to prevent the (unlikely)
case of someone inheriting from `Element` mark the class as `final`.

wrap/openfbx/src/ofbx.cpp

@@ -355,7 +355,7 @@ struct Property : IElementProperty
 };
 
 
-struct Element : IElement
+struct Element final : IElement
 {
 	IElement* getFirstChild() const override { return child; }
 	IElement* getSibling() const override { return sibling; }