Allow creating empty surfaces without using AppRegistry initialization paths (#48262)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/48262

Changelog: [internal]

At the moment, we can't start surfaces in Fabric without calling `AppRegistry.runApplication`.

This is completely unnecessary in cases like Fantom, where the creation of the surface is done manually from JS and we render to it immediately after (so we don't need to call into JS again to run AppRegistry).

Reviewed By: javache

Differential Revision: D67199971

fbshipit-source-id: e6402686b6f544a4a7651f6a21a57891ca6be3d1