Add Package.swift file to prebuild React native core (facebook#51197)

Summary:
Pull Request resolved: facebook#51197

This change adds the Package.swift file that can finally build React Native core using SPM

## Changelog:
[Internal] - Add Swift PM file to uild React Native Core using SwiftPM

Test Plan:
prepare the repo with
```
node packages/react-native/scripts/ios-prebuilds.js
```
and by downloading the ReactNativedependencies from the CI

Then open the Package.swift file in Xcode. I successfully built:
- iOS
- iOS Simulator
- Mac Catalyst

Reviewed By: lenaic

Differential Revision: D74393435

Pulled By: cipolleschi

fbshipit-source-id: 7d61ad1d09444a0c16e865062ae448ec1e7ef5ad

Author: chrfalch