Apply Nullsafe FIXMEs for xplat/js/react-native-github/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/turbomodule/core/TurboModuleManager.java (#50358)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50358

Added nullsafe FIXMEs for easier reviewing of next diff, where we fix them

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D71979595

fbshipit-source-id: 19bfcea537b7b62536eafa8e1d0b3f8b50666e22