Handle FCM tokenTask.exception nullability

When we upgrade to FCM 23.0.8 they changed the defintion to
tokenTask.exception to be possiblity null. Updated our code to
handle thier change.

Changes above also exposed the getToken defintion was out of sync with
between PushRegistratorAbstractGoogle and PushRegistratorFCM so this
was addressed.

Author: jkasten2

OneSignalSDK/onesignal/notifications/src/main/java/com/onesignal/notifications/internal/registration/impl/PushRegistratorAbstractGoogle.kt

@@ -34,6 +34,7 @@ import com.onesignal.notifications.internal.registration.IPushRegistrator
 import com.onesignal.user.internal.subscriptions.SubscriptionStatus
 import kotlinx.coroutines.delay
 import java.io.IOException
+import java.util.concurrent.ExecutionException
 
 /**
  * The abstract google push registration service.  It is expected [PushRegistratorFCM] will extend
@@ -47,7 +48,7 @@ internal abstract class PushRegistratorAbstractGoogle(
     IPushRegistrator, IPushRegistratorCallback {
     abstract val providerName: String
 
-    @Throws(Throwable::class)
+    @Throws(ExecutionException::class, InterruptedException::class, IOException::class)
     abstract suspend fun getToken(senderId: String): String
 
     override suspend fun registerForPush(): IPushRegistrator.RegisterResult {

OneSignalSDK/onesignal/notifications/src/main/java/com/onesignal/notifications/internal/registration/impl/PushRegistratorFCM.kt

@@ -128,7 +128,7 @@ internal class PushRegistratorFCM(
                 try {
                     token = Tasks.await(tokenTask)
                 } catch (e: ExecutionException) {
-                    throw tokenTask.exception
+                    throw tokenTask.exception ?: e
                 }
             }