[HigherOrderOp] expose torch.cond (#110293)
This pr expose torch._higher_order_ops.cond as torch.cond.
1. Need to add #noqa: F811 to the _check calls in torch/__init__.py to address some confusing linter error "Redefinition of unused 'cond'" but only one cond is imported and for these lines that have this error, they don't define the cond but just use it as an argument.
2. Also add cond to the list that allows it to be traced through so as dynamo could trigger the CondHigherOrder logic instead of creating a TorchVariable.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/110293
Approved by: https://github.com/zou3519
