Fix nondeterminism in torchgen (#82536)
Closes #82320
The iteration order of a `set` can change from run to run, resulting
in real content changes to generated files and therefore unnecessary
rebuilding.
The fix is to use a sort to give a repeatable iteration order.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82536
Approved by: https://github.com/ezyang
