Summary:
Adds three more tests:

* compare RN github ios and android flowconfigs
* compare xplat/js ios flowconfig with RN github ios flowconfig
* compare xplat/js android flowconfig with RN github android flowconfig

Reviewed By: TheSavior

Differential Revision: D9191176

fbshipit-source-id: 34f3644ffc5a26d3bdfd94b6c05a138407aaedeb