Refactor C->C to C->R twice (#55692)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55692
### Release notes
get_numerical_jacobian and get_analytical_jacobian only support `grad_out=1` and `fn` no longer accepts functions that return complex output
Test Plan: Imported from OSS
Reviewed By: H-Huang
Differential Revision: D28004614
Pulled By: soulitzer
fbshipit-source-id: 9592c9c69584b4035b39be62252f138dce39d3b5
