group constraints by arg (#101815)
Before, we would emit a soup of specializations / constraints without any obvious order to guide readability.
With this diff, we group such results by arg, and add comments preceding each group. Empirically, the results read much better.
Differential Revision: [D45995199](https://our.internmc.facebook.com/intern/diff/D45995199/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101815
Approved by: https://github.com/tugsbayasgalan
