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/test_pytorch_examples.py

@@ -25,8 +25,8 @@ from unittest.mock import patch
 import torch
 
 from transformers import ViTMAEForPreTraining, Wav2Vec2ForPreTraining
-from transformers.file_utils import is_apex_available
 from transformers.testing_utils import CaptureLogger, TestCasePlus, get_gpu_count, slow, torch_device
+from transformers.utils import is_apex_available
 
 
 SRC_DIRS = [