transition canned Estimators that are warm started from
        `tf.train.Optimizers` to `tf.keras.optimizers`.
    *   Losses are scaled in canned estimator v2 and not in the optimizers
        anymore. If you are using Estimator + distribution strategy + optimikzer
        v1 then the behavior does not change. This implies that if you are using
        custom estimator with optimizer v2, you have to scale losses. We have