Update on "opcheck should be usable without optional dependencies"

This PR excises opcheck's dependency on
torch.testing._internal.common_utils, (which comes with dependencies on
expecttest and hypothesis). We do this by moving what we need to
torch.testing._utils and adding a test for it.

Fixes #126870, #126871

Test Plan:
- new tests

[ghstack-poisoned]

torch/testing/_internal/common_utils.py

@@ -103,6 +103,10 @@
     has_pytest = False
 
 
+def freeze_rng_state(*args, **kwargs):
+    return torch.testing._utils.freeze_rng_state(*args, **kwargs)
+
+
 # Class to keep track of test flags configurable by environment variables.
 # Flags set here are intended to be read-only and should not be modified after
 # definition.

torch/testing/_utils.py

@@ -1,11 +1,13 @@
 import contextlib
+
 import torch
 from torch.utils._mode_utils import no_dispatch
 
 # Common testing utilities for use in public testing APIs.
 # NB: these should all be importable without optional dependencies
 # (like numpy and expecttest).
 
+
 def wrapper_set_seed(op, *args, **kwargs):
     """Wrapper to set seed manually for some functions like dropout
     See: https://github.com/pytorch/pytorch/pull/62315#issuecomment-896143189 for more details.