Add `federated_secure_sum` and `federated_secure_modular_sum` to the public API

PiperOrigin-RevId: 390627213

tensorflow_federated/__init__.py

@@ -40,11 +40,9 @@ from tensorflow_federated.python.core.impl.federated_context.intrinsics import f
 from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_eval
 from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_map
 from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_mean
+from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_secure_modular_sum
 from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_secure_select
-# TODO(b/191188806): Make this public once it is fully supported by MRF and
-# the test runtime.
-# from tensorflow_federated.python.core.impl.
-# federated_context.intrinsics import federated_secure_sum
+from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_secure_sum
 from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_secure_sum_bitwidth
 from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_select
 from tensorflow_federated.python.core.impl.federated_context.intrinsics import federated_sum