Make ExtraFilesMap return bytes instead of str (#43241)
Summary:
In case we want to store binary files using `ScriptModule.save(..., _extra_files=...)` functionality. With python3 we can just use bytes only and not bother about it.
I had to do a copy-pasta from pybind sources, maybe we should upstream it, but it'd mean adding a bunch of template arguments to `bind_map` which is a bind untidy.
Let me know if there's a better place to park this function (it seems to be the only invocation of `bind_map` so I put it in the same file)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43241
Reviewed By: zdevito
Differential Revision: D23205244
Pulled By: dzhulgakov
fbshipit-source-id: 8f291eb4294945fe1c581c620d48ba2e81b3dd9c
