prevent ANRs on background app event

Move calls to methods that do disk I/O from the main thread to a new
background thread.

There are reports where this can cause a significant amount of time on
main thread. Any disk I/O is a risk on the main thread and should not be
done as there is no upper bond of how long it can take. ANRs trigger
after 5 seconds of the main thread being busy.

The stacktrace of reported ANRs confirm that appStopped then calls
getSessionInfluences which can result in waiting on disk I/O.
We have also seen stacktraces with scheduling a AndroidX worker so
that was moved into this background thread as well. I isn't known if it
does any disk I/O but it was significant enough to show up in some ANRs

OneSignalSDK/onesignal/src/main/java/com/onesignal/ActivityLifecycleHandler.java

@@ -179,8 +179,14 @@ private void handleLostFocus() {
         if (focusHandler == null || focusHandler.hasBackgrounded() && !focusHandler.hasCompleted())
             return;
 
-        OneSignal.getFocusTimeController().appStopped();
-        focusHandler.startOnLostFocusWorker(FOCUS_LOST_WORKER_TAG, SYNC_AFTER_BG_DELAY_MS, OneSignal.appContext);
+        new Thread() {
+            public void run() {
+                // Run on it's own thread since both these calls do disk I/O
+                // which could contribute a significant amount to ANRs.
+                OneSignal.getFocusTimeController().appStopped();
+                focusHandler.startOnLostFocusWorker(FOCUS_LOST_WORKER_TAG, SYNC_AFTER_BG_DELAY_MS, OneSignal.appContext);
+            }
+        }.start();
     }
 
     private void handleFocus() {