Fix JDK java8 issue

see: https://bugs.openjdk.java.net/browse/JDK-8185328

Author: vkryachko

firebase-abt/src/main/java/com/google/firebase/abt/FirebaseABTesting.java

@@ -20,13 +20,10 @@
 
 import android.content.Context;
 import androidx.annotation.Nullable;
-import androidx.annotation.StringDef;
 import androidx.annotation.VisibleForTesting;
 import androidx.annotation.WorkerThread;
 import com.google.firebase.analytics.connector.AnalyticsConnector;
 import com.google.firebase.analytics.connector.AnalyticsConnector.ConditionalUserProperty;
-import java.lang.annotation.Retention;
-import java.lang.annotation.RetentionPolicy;
 import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -67,8 +64,9 @@ public class FirebaseABTesting {
    * Select keys of fields in the experiment descriptions returned from the Firebase Remote Config
    * server.
    */
-  @StringDef({REMOTE_CONFIG, INAPP_MESSAGING})
-  @Retention(RetentionPolicy.SOURCE)
+  // fully qualified use of annotations here due to https://bugs.openjdk.java.net/browse/JDK-8185328
+  @androidx.annotation.StringDef({REMOTE_CONFIG, INAPP_MESSAGING})
+  @java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.SOURCE)
   public @interface OriginService {
 
     /** Must match the origin code in Google Analytics for Firebase. */