*   TF Core:
    *   Added `tf.lookup.experimental.MutableHashTable`, which provides a
        generic mutable hash table implementation.
        *   Compared to `tf.lookup.experimental.DenseHashTable` this offers
            lower overall memory usage, and a cleaner API. It does not require
            specifying a `delete_key` and `empty_key` that cannot be inserted
            into the table.