Support optional float parameters (float?, optional<double>). (#31517)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31517
This is going to be used by upsample (which currently uses magic values to represent optionals).
For now, we just introduce a fake function for testing (torch._test_optional_float(x)).
Test Plan: Imported from OSS
Differential Revision: D19198721
Pulled By: gchanan
fbshipit-source-id: 0a1382fde0927c5d277d02d62bfb31fb574b8c74
