RN: Flowify `packages/react-native-codegen` (#51781)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/51781

Adds `flow` to the remaining files that are lacking it in the `packages/react-native-codegen` directory.

This also adds any necessary type annotations (using comment syntax).

Changelog:
[Internal]

Reviewed By: huntie

Differential Revision: D75884727

fbshipit-source-id: 69e880b2dc63c3d6430f841652506e57436544a8