Fix: localization dashboard on Windows
Summary
This fixes the localization dashboard on Windows by correctly converting the separator used in the slug into the corresponding filesystem separator.
Problem
The localization dashboard (ex. http://localhost:3000/fr/_translations/dashboard?section=/Web/JavaScript ) was not working on Windows and displayed progress bars in an undefined state.
Solution
Fix calls to document.findAll() to make sure the folderSearch was a folder path as expected on the OS filesystem.
N.B.
How did you test this change?
Ran it locally on a Windows (and on a Linux) machine (ex. opening http://localhost:3000/fr/_translations/dashboard?section=/Web/CSS after a yarn dev)
cc @mdn/localization-team-leads
Before:

After:

I tested on OSX and works fine
I'm not a windows user, but nice to see it works on it, @SphinxKnight thanks!
Thanks @SphinxKnight! 🎉