[jit] Make torch::utils::Future and ivalue::future apis closer (#35849)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35849
This change harmonizes some aspects of the api.
- torch::utils::Future callback should have no args, like ivalue::future.
Many of the lines of this change are related to fixing that up downstream.
No args makes the api simpler to use, particularly since many/most of the
downstream use cases ignore the passed-in args. It's simple enough to
appropriately capture the future in the lambda if necessary.
- Add error/hasError methods to ivalue::Future.
- Use c10::optional underneath for error to ivalue::Future.
- Change markCompleted(error) to setError(error) to ivalue::Future.
- Add setValue(FutureError) version to torch::utils::Future
ghstack-source-id: 101684435
Test Plan: buck test mode/dev-nosan caffe2/test/...
Differential Revision: D20803251
fbshipit-source-id: e3d925287bd9a80d649843eef5f270163f448269
