fix: Importing of project into Swift projects

[Brett-Best]

Description

Fixes #2158 by making C++ headers project instead of public.
Original code sample (in the issue) can be updated to include this change verifying the fix.

Checklist

• Included code example that can be used to test this change
• Updated TS types
• Updated documentation:
  • https://github.com/software-mansion/react-native-screens/blob/main/guides/GUIDE_FOR_LIBRARY_AUTHORS.md
  • https://github.com/software-mansion/react-native-screens/blob/main/native-stack/README.md
  • https://github.com/software-mansion/react-native-screens/blob/main/src/types.tsx
  • https://github.com/software-mansion/react-native-screens/blob/main/src/native-stack/types.tsx
• Ensured that CI passes

[kkafar]

Hi @Brett-Best, thanks for taking your time to introduce these changes 🎉 We will test these changes in reanimated context, because they are main consumers of this API and if it goes smoothly we can proceed with merging. FYI next release should be coming next week (in positive scenario).

[Brett-Best]

Thanks, it might be worth including import RNScreens in an example project or something that can be ran on CI to prevent breaking importing the library in the future.

[kkafar]

It seems we're fine on front of reanimated interop & also seems that it works well in runtime. Thanks!