Summary:
This Diff splits the `generate-specs-cli.js` script into:
* `generate-specs-cli-executor.js`: which contains the logic to generate the code for iOS.
* `generate-specs-cli.js`: which contains the argument parsing logic and invokes the executor.
Finally it introduces some tests.
## Changelog
[iOS][Changed] - Refactor part of the codegen scripts and add tests.
Reviewed By: cortinico, dmitryrykun
Differential Revision: D35892576
fbshipit-source-id: 6a3205af049bf55aa4ecaf64544ebc4eb7b13f73
Riccardo Cipolleschi