Consider en@quot on Windows

[hadley]

Continuing from discussion from https://github.com/MichaelChirico/potools/pull/234#issuecomment-962698623

The source claims it's only run in UTF8 locale because "substr()" needs to count UTF-8: https://github.com/wch/r-source/blob/430360aa394b02046dd7175c0fc55e347e947f80/src/library/tools/R/translations.R#L21-L22. But I don't think that's true any longer (as long as the encoding of the string is correct), so I think it's worth trying to run unconditionally, and if that doesn't work, providing a version of en_quote() that does work.

[MichaelChirico]

Happy to try! If it works, that should be reflected back to r-devel as well.