Capture API level during initialization

Author: aurimasc

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

@@ -547,6 +547,7 @@ public class AndroidNotificationCenter
 
         private static AndroidJavaObject s_CurrentActivity;
         private static JniApi s_Jni;
+        private static int s_ApiLevel;
         private static bool s_Initialized = false;
 
         /// <summary>
@@ -575,6 +576,9 @@ public static bool Initialize()
             var notificationManager = notificationManagerClass.CallStatic<AndroidJavaObject>("getNotificationManagerImpl", s_CurrentActivity, new NotificationCallback());
             s_Jni = new JniApi(notificationManagerClass, notificationManager);
 
+            using (var version = new AndroidJavaClass("android/os/Build$VERSION"))
+                s_ApiLevel = version.GetStatic<int>("SDK_INT");
+
             s_Initialized = true;
 #endif
             return s_Initialized;