Excise yaml dependency in torchgen.model (#100203)
The problem:
- The new CustomOp API depends on torchgen.model
- torchgen.model imports `yaml`
- `yaml` is not a PyTorch runtime dependency
To unblock myself, because I'm not sure how long it'll take to
convince people yaml should be a PyTorch runtime dependency
(unless one of you wants to approve #100166), this PR removes the
yaml dependency from torchgen.model.
It does so by splitting torchgen.utils (the offender) into
torchgen.utils (no yaml) and torchgen.yaml (which uses yaml).
Test Plan:
- CI
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100203
Approved by: https://github.com/ezyang, https://github.com/Skylion007
