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

utils/check_dummies.py

@@ -113,7 +113,7 @@ def create_dummy_files():
         backend_name = "[" + ", ".join(f'"{b}"' for b in backend.split("_and_")) + "]"
         dummy_file = "# This file is autogenerated by the command `make fix-copies`, do not edit.\n"
         dummy_file += "# flake8: noqa\n"
-        dummy_file += "from ..file_utils import DummyObject, requires_backends\n\n"
+        dummy_file += "from ..utils import DummyObject, requires_backends\n\n"
         dummy_file += "\n".join([create_dummy_object(o, backend_name) for o in objects])
         dummy_files[backend] = dummy_file