public static TestBeanBinder.PublicInterface create() {
        return new PrivateImplementation();
    }
Factory class that creates an instance whose type inherits from a public type (PublicInterface) but is of a type that is
inaccessible itself outside of its subpackage.

This is used to verify that such instances' methods can be accessed via BeanBinding in the same way that they can be accessed
outside of the package via polymorphism.
sqlobject/src/test/java/org/jdbi/v3/sqlobject/subpackage/PrivateImplementationFactory.java