cudagraphs dynamo backend (#80566)
This backend handles cases where the preexisting cuda graphs
implementation from dynamo is unsound/has errors.
Requires this functorch bug fix: https://github.com/pytorch/functorch/pull/935
Signed-off-by: Edward Z. Yang <ezyangfb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80566
Approved by: https://github.com/ngimel, https://github.com/wconstab
