Flax Big Bird (#11967)

* add flax bert

* bert -> bigbird

* original_full ported

* add debugger

* init block sparse

* fix copies ; gelu_fast -> gelu_new

* block sparse port

* fix block sparse

* block sparse working

* all ckpts working

* fix-copies

* make quality

* init tests

* temporary fix for FlaxBigBirdForMultipleChoice

* skip test_attention_outputs

* fix

* gelu_fast -> gelu_new ; fix multiple choice model

* remove nsp

* fix sequence classifier

* fix

* make quality

* make fix-copies

* finish

* Delete debugger.ipynb

* Update src/transformers/models/big_bird/modeling_flax_big_bird.py

* make style

* finish

* bye bye jit flax tests

Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

tests/test_modeling_flax_clip.py

@@ -342,6 +342,7 @@ class FlaxCLIPModelTest(FlaxModelTesterMixin, unittest.TestCase):
     def test_hidden_states_output(self):
         pass
 
+    @slow
     def test_jit_compilation(self):
         config, inputs_dict = self.model_tester.prepare_config_and_inputs_for_common()