Summary: This is a simple hook to allow native side to fetch any file under the js root folder via packager. Historically, only the `main.jsbundle` is fetched via the packager. This then allows fetching local file like a json file that lives under the same root js folder
Reviewed By: yungsters
Differential Revision: D4037730
fbshipit-source-id: a2d6eb5e30d148fee573d413fc4036d0189f4938
150c522be9