the specific way to accomplish this is touchy.
see <https://github.com/EmbarkStudios/rust-gpu/issues/312#issuecomment-738824131>:
> So I'd say placing any of the spirv_std::storage_class types into an aggregate (including capturing it in a closure) is unsupported for now
in our specific case, we can't return a tuple where one element is a `&`
to a spirv Input, and another element is a `&mut` to a spirv Output.
when we have a struct, it can enclose either ONLY inputs,
or ONLY outputs -- not a mix.
i'm not 100% on how the Serialized stuff works, since it appears to
violate that. i guess that's exactly what this ArrayHandle stuff
achieves though.
this solves an issue in the Nix build, where managing multiple
Cargo.lock files is otherwise tricky. it causes (or fails to fix?) an adjacent issue where
the spirv builder doesn't seem to have everything it needs vendored.
