Fix Compatibility with FCM (Firebase Messaging) 22.0.0

[jkasten2]

Description

One Line Summary

To fix FCM push token registration when using Firebase Cloud Messaging version 22.0.0 switched to using the newer FirebaseMessaging.getToken API instead of FirebaseInstanceId.getToken which has been completely removed in that version.

Details

• See commit-by-commit for additional details.

Fixes

The reported symptom of this is any fresh installs getting registered to OneSignal as not subscribed and without a push token. And seeing something like this in the logcat:

E/OneSignal: Unknown error getting FCM Token
    java.lang.NoClassDefFoundError: Failed resolution of: Lcom/google/firebase/iid/FirebaseInstanceId;
        at com.onesignal.PushRegistratorFCM.getToken(PushRegistratorFCM.java:62)
        at com.onesignal.PushRegistratorAbstractGoogle.attemptRegistration(PushRegistratorAbstractGoogle.java:97)
        at com.onesignal.PushRegistratorAbstractGoogle.access$100(PushRegistratorAbstractGoogle.java:37)
        at com.onesignal.PushRegistratorAbstractGoogle$1.run(PushRegistratorAbstractGoogle.java:84)
        at java.lang.Thread.run(Thread.java:919)
     Caused by: java.lang.ClassNotFoundException: Didn't find class "com.google.firebase.iid.FirebaseInstanceId" on path: DexPathList[[zip file "/data/app/com.onesignal.sdktest-MGzr3O5PDJapVYPx3JqH6Q==/base.apk"],nativeLibraryDirectories=[/data/app/com.onesignal.sdktest-MGzr3O5PDJapVYPx3JqH6Q==/lib/arm64, /system/lib64, /system/product/lib64]]
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:196)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:312)

Tests

Manual

• Tested app with firebase-messaging:19.0.0 with minifyEnabled true
• Tested app with firebase-messaging:22.0.0 with minifyEnabled true
• Ensured a fresh install shows as subscribed on the OneSignal dashboard.
• Ensured a push notification successfully displays

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This change is 

[Jeasmine]

LGTM!