[Static Runtime] SR clones graph input (#63704)

[Static Runtime] SR clones graph input (#63704)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63704

Previously SR did not clone the graph. This was leading to subtle bugs in `testStaticRuntime`; static runtime would modify its graph, and the graph used by the JIT interpreter would change as well. The JIT interpreter would then crash if SR-only ops were added!

Cloning the graph is more consistent with the behavior of the `Module` ctor.

Test Plan: `buck test caffe2/benchmarks/static_runtime/...`

Reviewed By: hlu1

Differential Revision: D30463294

fbshipit-source-id: b771551a1f55f95fde79373b23babcf3e5ddf726