Expose ReactDelegate for react-native-restart (#43588)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/43588

Supported `reload()` in Bridgeless through ReactDelegate in https://github.com/facebook/react-native/pull/43521 in order to unblock react-native-restart

https://github.com/avishayil/react-native-restart/blob/134cabd5b3f355ffe551e5dd1be1dd46d870fe13/android/src/main/java/com/reactnativerestart/RestartModule.java#L54

which can access React Delegate through :
```
if(currentActivity instanceof ReactActivity) {
    ReactActivity reactActivity = (ReactActivity) currentActivity;
    ReactDelegate reactDelegate = reactActivity.getReactDelegate();
    reactDelegate.reload()
}
```

Changelog:
[Android][Added] Expose ReactDelegate in ReactActivity

Reviewed By: cortinico

Differential Revision: D55166962

fbshipit-source-id: 5d8dfd7ad61edbcb5233014800eb66a538842ca5