Sharing assets with the underlying platform: Loading Flutter assets in Android

On Android the assets are available via the AssetManager API. The lookup key used in, for instance openFd, is obtained from lookupKeyForAsset on PluginRegistry.Registrar or getLookupKeyForAsset on FlutterView. PluginRegistry.Registrar is available when developing a plugin while FlutterView would be the choice when developing an app including a platform view.