Update serving code to enable saved_model=True (#18153)

* Add serving_output and serving methods to some vision models

* Add serving outputs for DeiT

* Don't convert hidden states - differing shapes

* Make saveable

* Fix up

* Make swin saveable

* Add in tests

* Fix funnel tests (can't convert to tensor)

* Fix numpy call

* Tidy up a bit

* Add in hidden states - resnet

* Remove numpy

* Fix failing tests - tensor shape and skipping tests

* Remove duplicated function

* PR comments - formatting and var names

* PR comments
Add suggestions made by Joao Gante:
* Use tf.shape instead of shape_list
* Use @tooslow decorator on tests
* Simplify some of the logic

* PR comments
Address Yih-Dar Sheih comments - making tensor names consistent and make types float

* Types consistent with docs; disable test on swin (slow)

* CI trigger

* Change input_features to float32

* Add serving_output for segformer

* Fixup

Co-authored-by: Amy Roberts <amyeroberts@users.noreply.github.com>

tests/models/clip/test_modeling_tf_clip.py

@@ -606,11 +606,21 @@ class TFCLIPModelTest(TFModelTesterMixin, unittest.TestCase):
             model = TFCLIPModel.from_pretrained(model_name)
             self.assertIsNotNone(model)
 
+    @unittest.skip(reason="Currently `saved_model` doesn't work with nested outputs.")
+    @slow
+    def test_saved_model_creation(self):
+        pass
+
     @unittest.skip(reason="Currently `saved_model` doesn't work with nested outputs.")
     @slow
     def test_saved_model_creation_extended(self):
         pass
 
+    @unittest.skip(reason="`saved_model` doesn't work with nested outputs so no preparation happens.")
+    @slow
+    def test_prepare_serving_output(self):
+        pass
+
 
 # We will verify our results on an image of cute cats
 def prepare_img():