bug fix for node with writers in create autodiff subgraph (#18491)

bug fix for node with writers in create autodiff subgraph (#18491)

Summary:
Previously we were moving nodes with writers into differentiable subgraphs, without necessarily preserving whether or not they were written to. This can lead to bugs with CSE, which needs that context.

I'm not completely sure if there's anything else we can do to be more aggresive here - inline these nodes and not run CSE and just run constant pooling, or possibly something else, but I think we should land this correctness condition first and then possibly think further.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18491

Differential Revision: D14648562

Pulled By: eellison

fbshipit-source-id: bc1e444774ccdb708e22f0e06a477a221a231f9e