[firebase_messaging]Added modern iOS notification types

[kflip]

New authorization options (formerly known as UIUserNotificationType) have been provided by apple with iOS10 and iOS12:
provisional (aka: silent notification), criticalAlert, notificationSetting and carPlay

This pull request intends to be backwards compatible until iOS8. Registering of any UIUserNotificationType or UNAuthorizationOptions is possible, if the operating system supports it.

A basic implementation of UNUserNotificationCenter for iOS10+ was necessary to request permission for these new types.

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[googlebot]

CLAs look good, thanks!

[kflip]

The tests fail since they are done with Xcode9 and iOS11. Is there a chance to update the test hosts?

[yevyevyev]

It's almost a year, the methods are deprecated, messaging needs this feature

[cyanglaz]

flutterfire has been re-homed to https://github.com/FirebaseExtended/FlutterFire
Please feel free to open a PR there, thanks.
I'm closing this PR here.