Why

#22638
https://linear.app/expo/issue/ENG-6296/add-event-based-hooks-to-expo-localization-to-allow-listening-to

How

Hooks (https://linear.app/expo/issue/ENG-6296/add-event-based-hooks-to-expo-localization-to-allow-listening-to)

We add hooks to JS and event listeners on native side.
On iOS it's easy as we can just use NotificationCenter.

On Android we need to add |locale|layoutDirection to [configChanges](android:configChanges).
To do this we need to add a mod to a config plugin.
We also need to use the old Package api and create a static notifier object that will inform our Module that a Package has received a onConfigurationChanged event.

User settings (#22638)

We take two separate locales, and for settings that are overridable by the user (decimal separators, number separators, ect.) we use the current locale instead of the locale computed from the language.

I'm not confident this is the best solution.
On Android it's just a list of locales, on iOS we get one locale and a list of preferred languages. There's also no way to check if settings are default for the locale or overridden by the user.

Other options:

• Only override the locale defaults for the first locale on the list – if an app only supports locale US perhaps it should also format numbers in the US way.

Test Plan

Tested manually in a standalone app – this makes both Android and iOS update locale settings without loosing react state.

Checklist

• Documentation is up to date to reflect these changes (eg: https://docs.expo.dev and README.md).
• Conforms with the Documentation Writing Style Guide
• This diff will work correctly for npx expo prebuild & EAS Build (eg: updated a module plugin).