Move TorchDynamo into PyTorch core (#86461)
Context:
https://github.com/pytorch/torchdynamo/issues/1588
This PR moves [TorchDynamo](https://github.com/pytorch/torchdynamo) and TorchInductor into PyTorch core.
- `torchdynamo` becomes `torch._dynamo`
- `torchinductor` becomes `torch._inductor`
This PR was generated by running `copy_to_core.sh` in https://github.com/pytorch/torchdynamo/pull/1538
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86461
Approved by: https://github.com/voznesenskym
