Restore legacy semantics of modulesConformingToProtocol (#51381)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/51381

Changelog: [General][Fixed] Fixed codegen breaking when a subset of `modulesConformingToProtocol` fields was specified or when the value was string

D70822061 introduced a new way of defininf modules and components in codegen, but accidentally introduced two breaking changes to the legacy syntax:
- before that diff, in case of 1:1 mapping, the value of the fileds could be a string, while after, it required it to be an array
- before that diff, not all of the fields on `modulesConformingToProtocol` had to be defined in `package.json`, while after, it required all fields to be defined even if unused

Reviewed By: cipolleschi

Differential Revision: D74875251

fbshipit-source-id: 610103b508f1462b4de01725f9b0a87341571197