*   Make calls to `tf.function(f)()`, `tf.function(f).get_concrete_function`
        and `tf.function(f).get_initialization_function` thread-safe.
    *   Extend `tf.identity` to work with CompositeTensors (such as
        SparseTensor)
    *   Added more `dtypes` and zero-sized inputs to `Einsum` Op and improved
        its performance
    *   Enable multi-worker `NCCL` `all-reduce` inside functions executing