it from V2, and added `tf.compat.v1.data.make_initializable_iterator()`.
    *   Enable nested dataset support in core `tf.data` transformations.
    *   For `tf.data.Dataset` implementers: Added
        `tf.data.Dataset._element_structured property` to replace
        `Dataset.output_{types,shapes,classes}`.
    *   Make `num_parallel_calls` of `tf.data.Dataset.interleave` and