Generated DataObject interfaces should override DataObject.getImplementedClass()

We currently purely inherit this class, which is suboptimal when dealing with generics, most notably this case does not work:

interface Foo extends DataObject;

public <T extends Foo> void doSomething(T foo) {
    Class<? extends T> fooSubclass = foo.getImplementedInterface();
}

While all implementations are already returning the right answer (and if they don't Binding just breaks down), it is not expressed in the interface contract.

This this by generating a default interface method:

interface Foo extends DataObject {
    @Override
    default Class<? extends Foo> getImplementedInterface() {
        return Foo.class;
    }
}

This already exists in Builder's implementation generator, albeit in the form:

@Override
public Class<Foo> getImplementedInterface() {
    return Foo.class;
}