Fix the setup to allow the build-from-source on host projects (#36702)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/36702

With the monorepo changes we broke the build from source for users.
This fixes it so that folks can just follow the guide:
https://reactnative.dev/contributing/how-to-build-from-source

Changelog:
[Android] [Fixed] - Fix the setup to allow the build-from-source on host projects

Reviewed By: cipolleschi

Differential Revision: D44502428

fbshipit-source-id: 3ad8fb114f5e2f7ffdf6fffa617ceaa45334f5f3