Investigate push activation not completing on iOS when running in release configuration

[ben-xD]

When running the application in release mode, the device fails to complete activation when it first launches. The last event in the state machine is a transition from {{NotActivated}} to {{WaitingForPushDeviceDetails}}. A workaround would be to close and relaunch the app. Once relaunched, activation/deactivation works.

{code}
2021-12-06 15:00:34.685283+0700 Runner[21776:7802732] DEBUG: ARTPushActivationStateMachine: transition: ARTPushActivationStateNotActivated -> ARTPushActivationStateWaitingForPushDeviceDetails
{code}
To reproduce it:

• Run the example app using either
  ** {{flutter run --dart-define=ABLY_API_KEY=$ABLY_API_KEY --release}}.
  ** Xcode "release" configuration and debug executable unchecked (see screenshot)
  !https://user-images.githubusercontent.com/24711048/144826023-3348d069-3482-4c32-9511-98a32d3a17d8.png|CleanShot 2021-12-06 at 09 58 04!
• Attempt to activate the device by scrolling down to the "Push Notifications" sliver of the scroll view, and press "Activate"
• You should notice nothing happening. This is because the Future does not complete, because Ably Cocoa never calls back the {{result}} in the following code:
  

  ably-flutter/ios/Classes/handlers/PushActivationEventHandlers.swift

  Lines 34 to 45 in 8e85a88

  	public func didActivateAblyPush(_ error: ARTErrorInfo?) {
  	defer {
  	flutterResultForActivate = nil
  	}
  	methodChannel.invokeMethod(AblyPlatformMethod_pushOnActivate, arguments: error, result: nil)
  	if let result = flutterResultForActivate {
  	result(error)
  	} else {
  	print("Did not return a value asynchronously because flutterResultForActivate was nil. The app might have been restarted since calling activate.")
  	}
  	}

Other notes:

• This only happens on iOS
• Other platform methods are working (e.g. connect realtime).

h1. Problem?
This requires further investigation.

This might it is an Ably Cocoa, specifically an Activation State Machine issue, potentially a race condition which occurs when the app runs faster (e.g. in release mode).

[ben-xD]

After further investigation, it looks like it is because the APNs token is not provided to the app early enough in some cases, and the realtime and rest clients are instantiated without it.

To test this out, use:

  ably_flutter:
    git:
      url: git://github.com/ably/ably-flutter.git
      ref: 4685ad628509ca4261c1a283fdc2c90a8fc2cdd0