Add test to ensure setUpDefaultReactNativeEnvironment does not access feature flags (#53057)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/53057

Changelog: [internal]

This adds a Fantom test to ensure that `setUpDefaultReactNativeEnvironment` doesn't read any feature flags. This prevents catching this as a runtime issue when the feature flag system complains that feature flags were accessed before being overridden, which always would happen if this module read any flags (as it runs before any product code that sets overrides).

Reviewed By: rshest

Differential Revision: D79639890

fbshipit-source-id: 6997609b7bf84947a6da53b58e68f9edd5654912