Explicitly declare app language and support per-app language preferences

[auroursa]

Based #6567

It seems that CFBundleLocalizations is not the only factor affecting iOS when providing a localized text input context menu. According to this documentation, we also need to create a Localization.strings file to list the supported languages for the app.

On Android, the system language settings determine the localized text input context menu, not by app’s declaration. But creating a language list file can enable per-app language preferences on Android.

By introducing this react-native-localization-settings package, we can generate the language list files for both Android and iOS, while it also performing additional tasks to compatibility with system APIs.

In the Chinese section of the language list, following up on #6621, I used the RFC 4646 standard, as both iOS and Android prefer it, and it also complies with IETF BCP 47.

This should fix #6162 again.