Make codegen generate a Package.swift file for Codegen'd target (#53619)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/53619

With this change, we are making Codegen generate a Package.swift file so that we can integrate the `ReactCodegen` and the `ReactAppDependencyProvider` in apps only using SwiftPM

## Changelog
[iOS][Added] - Make codegen generate PAckage.swift file for the codegen targets

Reviewed By: cortinico

Differential Revision: D81769543

fbshipit-source-id: 1f1a1b9f41126e142931d5eda6e75109a69f828c