Summary:
Add minimum necessary .d.ts files to react-native-codegen.
I found .d.ts files will be copied to `lib` so I guess no additional script is needed.
## Changelog
[GENERAL] [CHANGED] - Add minimum necessary .d.ts files to react-native-codegen
Pull Request resolved: https://github.com/facebook/react-native/pull/36102
Test Plan: `npm run build` in `packages/react-native-codegen` and see all .d.ts files appear in `lib`.
Reviewed By: cortinico
Differential Revision: D43157233
Pulled By: cipolleschi
fbshipit-source-id: 6f122f0f4cda693ba22af6dd534e9d34d069ecac
Zihan Chen (MSFT)