Add support for Python 3.8 Constant node (#22007)
Summary:
We can't really test these until we get Python 3.8 in the CI, but these all work locally and won't be invoked at all for Python 3.7 and lower so this should be pretty safe.
Fixes #21710
](https://our.intern.facebook.com/intern/diff/15914735/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22007
Pulled By: driazati
Differential Revision: D15914735
fbshipit-source-id: 83833cebe7e38b162719a4f53cbe52c3fc638edd
