Update codegen to support namespaced types (facebook#49950)

Summary:
Pull Request resolved: facebook#49950

Changelog: [GENERAL][CHANGED] - Changed `react-native-codegen` to support types under `CodegenTypes` namespace

## Summary

Currently, codegen relies on deep importing types under `react-native/Libraries/Types/CodegenTypes` to be properly type-checked. Updating codegen to support types under a single namespace will enable us to provide a single import from the package with access to all relevant types.

Reviewed By: huntie

Differential Revision: D70967809

fbshipit-source-id: 41241dcc51965f4243acd34e8b63475cb56ca67a

Author: j-piasecki