Add is_inference to native functions (#58729)
Summary:
Adds `is_inference` as a native function w/ manual cpp bindings.
Also changes instances of `is_inference_tensor` to `is_inference` to be consistent with other properties such as `is_complex`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58729
Reviewed By: mruberry
Differential Revision: D28874507
Pulled By: soulitzer
fbshipit-source-id: 0fa6bcdc72a4ae444705e2e0f3c416c1b28dadc7
