Add generate() functionality to TF 2.0 (#3063)

* add first copy past test to tf 2 generate

* add tf top_k_top_p_filter fn

* add generate function for TF

* add generate function for TF

* implemented generate for all models expect transfoXL

* implemented generate for all models expect transfoXL

* implemented generate for all models expect transfoXL

* make style

* change permission of test file to correct ones

* delete ipdb

* delete ipdb

* fix bug and finish simple gpt2 integration test

* clean test file

* clean test file

* make style

* make style

* make style

* make style

* change import style

* change import style

* make style

* make style

* add decorators

* add decorators

* fix tf ctrl bug dim => axis in TF

* make style

* make style

* refactored test file

* refactored test file

* take out test_torch_tf_conversion if nothing is defined

* take out test_torch_tf_conversion if nothing is defined

* remove useless files

* remove useless files

* fix conflicts

* fix conflicts

* fix conflicts

* fix conflicts

* fix conflicts

* solve conflicts

* solve conflicts

* fix conflicts

* fix conflicts

* merge conflicts

* delete ipdb

* exposed top_k_top_p_filtering fns

* delete weirdly created w! file

* add comment to test tf common modeling

* fix conflicts

* fix conflicts

* make style

* merge conflicts

* make style

* change tf.tensor.shape to shape_list(tensor)

src/transformers/__init__.py

@@ -136,7 +136,7 @@ if is_sklearn_available():
 
 # Modeling
 if is_torch_available():
-    from .modeling_utils import PreTrainedModel, prune_layer, Conv1D
+    from .modeling_utils import PreTrainedModel, prune_layer, Conv1D, top_k_top_p_filtering
     from .modeling_auto import (
         AutoModel,
         AutoModelForPreTraining,
@@ -291,7 +291,13 @@ if is_torch_available():
 
 # TensorFlow
 if is_tf_available():
-    from .modeling_tf_utils import TFPreTrainedModel, TFSharedEmbeddings, TFSequenceSummary, shape_list
+    from .modeling_tf_utils import (
+        TFPreTrainedModel,
+        TFSharedEmbeddings,
+        TFSequenceSummary,
+        shape_list,
+        tf_top_k_top_p_filtering,
+    )
     from .modeling_tf_auto import (
         TFAutoModel,
         TFAutoModelForPreTraining,