Add Python container to the struct type so that the `tf_computation` does not return `tff.structure.Struct`.
Add Python container to the struct type so that the `tf_computation` does not
return `tff.structure.Struct`.

This is a necessary step to enabling auto-control-dependencies (ACD) in the
`tensorflow_wrapper`. ACD is not compatible with `tff.structure.Struct`.

PiperOrigin-RevId: 448297886

tensorflow/federated,tensorflow/federated,tensorflow/federated