Revert recent Flow syntax codemods in react-native-github (#56998)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56998

Reverts the recent Flow syntax codemods applied across `packages/`, `private/`, and `scripts/` in react-native-github. Specifically restores the previous form for:

- `+T` / `+Instance` style variance annotations on generic type parameters that had been converted to the newer `out T` / `in T` keyword form.
- `+field:` covariant object/interface properties that had been converted to the `readonly field:` modifier form.
- `+[K in keyof T]:` mapped-type covariance that had been converted to `readonly [K in keyof T]:`.

These are purely Flow type-annotation changes with no runtime behavior impact, restoring the form that the rest of the toolchain (in particular Fantom) already supports.

Changelog: [Internal]

Reviewed By: christophpurrer

Differential Revision: D106813102

fbshipit-source-id: 6bf915d530e130eba9c9d96a2b6c3dc8853594d1