TensorFlow Federated 0.83.0

Release 0.83.0

Changed

• The tff.learning.programs.train_model program logic to save a deep copy of
  the data source iterator within the program state.
• The file-backed native program components to not flatten and unflatten
  values.

Removed

• Unused functions from tensorflow_utils.
• Serializing raw tf.Tensor values to the Value protobuf.
• Partial support for dataclasses.