Use FB-specific renderers when running tests in Meta infra (#36877)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/36877

This diffs allows having Meta-specific tests and modules that are only used when running tests in Meta's infra. Meta-specific modules aren't synced to Github, so the OSS versions will be used when running tests on Github.

This is needed because we recently some files from React to React Native, including a test that now uses the `ReactFabric` module to test the behavior of public instances in React Native. This module is always using the OSS version of the renderer, but at Meta we have a custom version that's being ignored in tests.

Changelog: [internal]

Reviewed By: cortinico

Differential Revision: D44874631

fbshipit-source-id: e3112041f134240601495a28ba643bce45d802fb