Provide bridge methods from DocumentedNode to EffectiveStatement

Most of DocumentedNode subclasses have an equivalent EffectiveStatement. This is certainly true on the implementation side, where the same objects are implementing both aspects.

In order to allow users to migrate to EffectiveStatement world, we need to provide a bridge method, allowing to jump from, say, Module to ModuleEffectiveStatement:

interface Module {
    /**
     *
     * @throws UnsupportedOperationException
     */
    @NonNull ModuleEffectiveStatement asEffectiveStatement();
}