Reorganize file utils (#16264)

* Split file_utils in several submodules

* Fixes

* Add back more objects

* More fixes

* Who exactly decided to import that from there?

* Second suggestion to code with code review

* Revert wront move

* Fix imports

* Adapt all imports

* Adapt all imports everywhere

* Revert this import, will fix in a separate commit

examples/pytorch/summarization/run_summarization.py

@@ -45,9 +45,8 @@ from transformers import (
     Seq2SeqTrainingArguments,
     set_seed,
 )
-from transformers.file_utils import is_offline_mode
 from transformers.trainer_utils import get_last_checkpoint
-from transformers.utils import check_min_version
+from transformers.utils import check_min_version, is_offline_mode
 from transformers.utils.versions import require_version