Add partitioned nvFuser executor with ATen fallbacks (#81043)
This PR introduces a new nvFuser executor for FX graphs containing different kinds of nodes, not just `torch.ops.prims` supported by nvFuser. The FX graph is partitioned based on whether nodes are supported or not by nvFuser and supported nodes are fused into subgraphs, that's all using Sherlock's work on the partitioner.
This new partitions-based executor with fallbacks to ATen is used by default with `executor="nvfuser"`. And the previous executor can be used with `executor="strictly_nvfuser"`, naming suggestions are welcome!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81043
Approved by: https://github.com/jjsjann123, https://github.com/SherlockNoMad
