[FSDP] Fixed `device_mesh` and auto wrap (#119064)
If the user passes `device_mesh`, then we should not forward the process groups to the children during auto wrap and instead just rely on the `device_mesh` argument. This should fix https://github.com/pytorch/pytorch/issues/118906.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/119064
Approved by: https://github.com/wz337
