Binary instances for `OsString`, etc.

In GitLab by @phadej on Jul 17, 2022, 03:04

Where these should be?

1. `binary` (then `binary` would depend on `filepath`)
2. `filepath` (then `filepath` would depend on `binary`)
3. somewhere else? (https://hackage.haskell.org/package/binary-instances or new `filepath-binary-instances`).

I don't know if how GHC serializes its stuff, but I bet there are filepaths in there. (`Cabal` does, and uses `Generic`s). So that rules out third option, except if it's a new `filepath-binary-instances` package which is bundled with GHC.

Otherwise I'd prefer second option, so the type-class providing package stays as dependency-light as possible.

ping @bgamari