Reduce friction with multiple plugins are being registered as a UNUserNotificationCenterDelegate #22099
Description
Conflicts occur when multiple plugins register themselves as UNUserNotificationCenterDelegate e.g. one for display local notification and one for Firebase. Is there a way around that? It'd be good if the engine could provide a solution as there are similar mechanisms already (e.g. see https://docs.flutter.io/objcdoc/Protocols/FlutterPluginRegistrar.html). Having a similar method for the UNUserNotificationCenterDelegate would help reduce friction that would make it easier for developers to write code on iOS for displaying notifications without having to look at something like method swizzling.
[✓] Flutter (Channel beta, v0.8.2, on Mac OS X 10.13.6 17G65, locale en-AU)
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