[Redesign] Rebuild Roboto Slab

Summary: Ref T8755. Hunting down some display issues with the fonts on certain computers (Ubuntu, Windows, Chrome Mobile). Hopefully having the full font fallback tree will resolve the issues.

Test Plan: Review Phriction on my Mac, no distinguishable difference. Will test Ubuntu after it lands.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8755

Differential Revision: https://secure.phabricator.com/D13552