Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/34176
It extracts the code related to the codegen from the main `react_native_pods` script to a dedicated file, adding also tests.
## Changelog
[iOS][Changed] - Move codegen in separate files
Reviewed By: cortinico
Differential Revision: D37755818
fbshipit-source-id: 99760d1def26ddbf065fdd234e0d183c2795513c