Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/33818
This Diff moves the fabric setup from the `react_native_pods` script to its own `fabric` file.
It also introduces tests for the file and some test utilities.
## Changelog
[iOS][Changed] - Move fabric setup to its own file
Reviewed By: cortinico, dmitryrykun
Differential Revision: D36344911
fbshipit-source-id: 586186684be2c0080f247390f26145f2defa9e97
Riccardo Cipolleschi