Apply ufmt linter to all py files under torchgen (#81570)
Previous batches:
* https://github.com/pytorch/pytorch/pull/81285
* https://github.com/pytorch/pytorch/pull/81335
We have multiple batches here to minimize merge conflicts and reviewing process. Once everything has been formatted by ufmt (black+usort), the current black linter will be removed.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81570
Approved by: https://github.com/ezyang
