Fix TF s2s models (#9478)

* Fix Seq2Seq models for serving

* Apply style

* Fix lonfgormer

* Fix mBart/Pegasus/Blenderbot

* Apply style

* Add a main intermediate layer

* Apply style

* Remove import

* Apply tf.function to Longformer

* Fix utils check_copy

* Update S2S template

* Fix BART + Blenderbot

* Fix BlenderbotSmall

* Fix BlenderbotSmall

* Fix BlenderbotSmall

* Fix MBart

* Fix Marian

* Fix Pegasus + template

* Apply style

* Fix common attributes test

* Forgot to fix the LED test

* Apply Patrick's comment on LED Decoder

tests/test_modeling_tf_bart.py

@@ -264,22 +264,8 @@ class TFBartModelTest(TFModelTesterMixin, unittest.TestCase):
                                 models_equal = False
                     self.assertTrue(models_equal)
 
-    @slow
-    def test_saved_model_with_hidden_states_output(self):
-        # TODO(JPLU, PVP) - fix this with s2s tf-serving PR
-        pass
-
-    @slow
-    def test_saved_model_with_attentions_output(self):
-        # TODO(JPLU, PVP) - fix this with s2s tf-serving PR
-        pass
-
     def test_saved_model_creation(self):
-        # TODO(JPLU, PVP) - fix this with s2s tf-serving PR
-        pass
-
-    def test_saved_model_creation_extended(self):
-        # TODO(JPLU, PVP) - fix this with s2s tf-serving PR
+        # This test is too long (>30sec) and makes fail the CI
         pass