Summary:
Add the `react-native-codegen` source to the `react-native` npm package.
Instead of using `react-native-codegen` from npm, the iOS app template will now build the package from source. Doing so removes the need to carefully time `react-native-codegen` npm releases to oss `react-native` releases, as the codegen and the oss release will be cut at the same time.
Changelog: [Internal] - Removed react-native-codegen dependency from iOS app template
Reviewed By: TheSavior
Differential Revision: D24904655
fbshipit-source-id: a07932bc748e2afb9359de584181bcb9dd0810ea
Kevin Gozali
58c80d4f8d