useful to regenerate in a single call the compiled training function
        when any `.trainable` attribute of any model's layer has changed.
    *   Models now have a `save_spec` property which contains the `TensorSpec`
        specs for calling the model. This spec is automatically saved when the
        model is called for the first time.
*   `tf.linalg`:
    *   Add `CompositeTensor` as a base class to `LinearOperator`.
*   `tf.lite`: