Crash the app when Legacy Arch is enabled (#53911)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/53911

This change mimics what we implemented on Android to crash the app.

This is in general never going t be triggered. It will be triggered only if users are actually going through the old way to initialize React Native, i.e. by using the RCTRootView class which creates thebridge, or if they are creating the bridge themselves.

## Changelog:
[iOS][Added] - Crash the app if they force the legacy architecture.

Reviewed By: RSNara, cortinico

Differential Revision: D83066377

fbshipit-source-id: 0907effceb9a3655ec8d6bde8e0986f50f1ab663