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>
