Properly dispose player class once no longer needed

Author: aurimasc

com.unity.mobile.notifications/Runtime/Android/AndroidNotificationCenter.cs

@@ -568,8 +568,8 @@ public static bool Initialize()
 #if UNITY_EDITOR || !UNITY_ANDROID
             s_CurrentActivity = null;
 #elif UNITY_ANDROID
-            var unityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer");
-            s_CurrentActivity = unityPlayer.GetStatic<AndroidJavaObject>("currentActivity");
+            using (var unityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer"))
+                s_CurrentActivity = unityPlayer.GetStatic<AndroidJavaObject>("currentActivity");
 
             var notificationManagerClass = new AndroidJavaClass("com.unity.androidnotifications.UnityNotificationManager");
             var notificationManager = notificationManagerClass.CallStatic<AndroidJavaObject>("getNotificationManagerImpl", s_CurrentActivity, new NotificationCallback());