Add a method to generate a temp podspec
Add a method to generate a temp podspec

Summary:
The new architecture generates code that needs to be included in the xcode project. This diff adds a method that will be called when calling "pod install". There will be following diffs that will add the usage of this function.

Changelog: [internal]

Reviewed By: hramos

Differential Revision: D31699330

fbshipit-source-id: 491de7f60afee69aae750bbda6a687cea2526cc0

javache/react-native,janicduplessis/react-native,javache/react-native,facebook/react-native,javache/react-native,javache/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,janicduplessis/react-native,javache/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,janicduplessis/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native,javache/react-native,facebook/react-native,javache/react-native