[FX] Support tensor-valued constants (#43666)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/43666
Test Plan: Imported from OSS
Reviewed By: dzhulgakov
Differential Revision: D23359110
Pulled By: jamesr66a
fbshipit-source-id: 8569a2db0ef081ea7d8e81d7ba26a92bc12ed423
