[NativeScript] added global type tag system

[karroffel]

This adds a map for library-defined global type tags. This is useful for safe casting and type checking on the library side.

[Zylann]

How is it working for testing base class types? For example, if the function expects a CustomSprite, but you are passing a CustomAnimatedSprite (which however inherits CustomSprite)?

[karroffel]

This global type tag system is not intended to be used with custom classes. It's there to tag all objects with a value that the language bindings can work with, so when you pass a CustomSprite, then the type tag generated for that wrapper will be for Sprite.

The check that you are describing is already possible with the type tag system on master.

This global system was added so that

Object *o = get_the_object();
Reference *r = Object::cast_to<Reference>(o);

works, but without this PR the language bindings would have to do name compares for this.