enable NVFuser by default
Enable NVFuser in OSS.
Tests are passing, and we've also run tests in [torchvision](https://github.com/pytorch/vision/pull/5959) and [torchaudio](https://github.com/pytorch/audio/pull/2372)
Retry of #76006, because that PR had GH1/ghstack issues.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77213
Approved by: https://github.com/eellison
