[ONNX] Cover 'undiscoverable' ops 'torch.ops.aten' (#99682)
Due to https://github.com/pytorch/pytorch/issues/99681, ops supported by torchlib in `function_dispatcher` may not get
registered. This PR works around it by doing reverse look up.
Also fixes aten signature for `log_sigmoid`, which appears to be an outlier with unique naming style.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99682
Approved by: https://github.com/titaiwangms, https://github.com/justinchuby
