WKWebView currently only has an API to remove all user scripts (`WKUserContentController.removeAllUserScripts()`). It would be useful if specific scripts could be specified for removal. At Brave, this would be helpful to remove user scripts based on specific pages, settings, or website behaviors. This would potentially require `addUserScript` to return a reference for removal later. Related Radar: https://openradar.appspot.com/FB7557869 (rdar://FB7557869)
<rdar://problem/59350824>