Adds get_full_class_name_T function to provide better introspection.

This commit adds the function get_full_class_name_T which can be overriden
by the exposed classes. The returned string is used to populate the __name
field of the exposed class metatable. This allows to provide better introspection
since we can provide the full name of the class (i.e. including the module name)
instead of just using exported class name.

By default, get_full_class_name_T will return the className unless overridden.