Fixing React Native WebView’s postMessage for iOS

The error that should have never been.

In 2016, GitHub user Robert Roskam (raiderrobert) opened an issue on the React Native repository reporting the error “Setting onMessage on a WebView overrides existing values of window.postMessage, but a previous value was defined”. In the two years since then, nothing has been done to resolve it within the internal React Native implementation of WebView.