New run glue script (#7917)

* Start simplification

* More progress

* Finished script

* Address comments and update tests instructions

* Wrong test

* Accept files as inputs and fix test

* Update src/transformers/trainer_utils.py

Co-authored-by: Julien Chaumond <chaumond@gmail.com>

* Fix labels and add combined score

* Add special labels

* Update TPU command

* Revert to old label strategy

* Use model labels

* Fix for STT-B

* Styling

* Apply suggestions from code review

Co-authored-by: Thomas Wolf <thomwolf@users.noreply.github.com>

* Code styling

* Fix review comments

Co-authored-by: Julien Chaumond <chaumond@gmail.com>
Co-authored-by: Thomas Wolf <thomwolf@users.noreply.github.com>

examples/test_xla_examples.py

@@ -44,8 +44,7 @@ class TorchXLAExamplesTests(unittest.TestCase):
             transformers/examples/text-classification/run_glue.py
             --do_train
             --do_eval
-            --task_name=MRPC
-            --data_dir=/datasets/glue_data/MRPC
+            --task_name=mrpc
             --cache_dir=./cache_dir
             --num_train_epochs=1
             --max_seq_length=128