OpInfo: Add DecorateInfo class similar to SkipInfo for decorators (#50501)
Summary:
Follow up to https://github.com/pytorch/pytorch/issues/50435
I have confirmed this works by running
```
pytest test_ops.py -k test_fn_gradgrad_fft`
```
with normally and with `PYTORCH_TEST_WITH_SLOW=1 PYTORCH_TEST_SKIP_FAST=1`. In the first case all tests are skipped, in the second they all run as they should.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50501
Reviewed By: ezyang
Differential Revision: D25956416
Pulled By: mruberry
fbshipit-source-id: c896a8cec5f19b8ffb9b168835f3743b6986dad7
