[Dynamo] Code refactor: move context managers out of misc.py (#97958)
misc.py and test_misc.py is too big, moving context managers to context.py and test_context.py.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97958
Approved by: https://github.com/ezyang, https://github.com/anijain2305, https://github.com/mlazos, https://github.com/voznesenskym
