Add support for SchemaKind.mutable to to_out_variant (#2541)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2541

Ideally custom mutator ops would not be in aten OpOverload but would instead be edge ops. The  pass that results in mutator ops being in the graph is shared with core for now though and its hard to mix and match EP passes and GM passes. So just add the logic to the otherwise unused aten to_out_variant code.

Reviewed By: larryliu0820

Differential Revision: D55156605

fbshipit-source-id: 3003a51b83bb211345c1d6c6e5bb7e97c19dfeb1