Summary: This is the first step in organizing React Native slightly differently. This doesn't set up a "monorepo" structure for the GitHub repo yet, it merely moves a few files around and I slightly updated the package.json file for the codegen project.
Reviewed By: rickhanlonii, TheSavior
Differential Revision: D13974180
fbshipit-source-id: f53375f3b6618ef12658064cb1fc690ef1f95299
