Summary:
React Native overrides the `metro.config.js` settings for, e.g., `hasteImplModulePath`, which prevents us from adding a `metro.config.js` file to the repo for `react-native-windows` to allow us to resolve Haste modules at the top-level of the repo. This change ensures that if a user has a `metro.config.js` file, those settings are not overwritten by React Native.
Pull Request resolved: https://github.com/facebook/react-native/pull/20705
Differential Revision: D9390146
Pulled By: hramos
fbshipit-source-id: 5ccc137490410ace72d7b0e68f2bafcbb233c59f