Change model outputs types to self-document outputs (#5438)

* [WIP] Proposal for model outputs

* All Bert models

* Make CI green maybe?

* Fix ONNX test

* Isolate ModelOutput from pt and tf

* Formatting

* Add Electra models

* Auto-generate docstrings from outputs

* Add TF outputs

* Add some BERT models

* Revert TF side

* Remove last traces of TF changes

* Fail with a clear error message

* Add Albert and work through Bart

* Add CTRL and DistilBert

* Formatting

* Progress on Bart

* Renames and finish Bart

* Formatting

* Fix last test

* Add DPR

* Finish Electra and add FlauBERT

* Add GPT2

* Add Longformer

* Add MMBT

* Add MobileBert

* Add GPT

* Formatting

* Add Reformer

* Add Roberta

* Add T5

* Add Transformer XL

* Fix test

* Add XLM + fix XLMForTokenClassification

* Style + XLMRoberta

* Add XLNet

* Formatting

* Add doc of return_tuple arg

tests/test_modeling_common.py

@@ -220,7 +220,6 @@ class ModelTesterMixin:
 
     def test_torchscript(self):
         config, inputs_dict = self.model_tester.prepare_config_and_inputs_for_common()
-
         self._create_and_check_torchscript(config, inputs_dict)
 
     def test_torchscript_output_attentions(self):
@@ -230,7 +229,6 @@ class ModelTesterMixin:
 
     def test_torchscript_output_hidden_state(self):
         config, inputs_dict = self.model_tester.prepare_config_and_inputs_for_common()
-
         config.output_hidden_states = True
         self._create_and_check_torchscript(config, inputs_dict)