Mark IWindowFocusObserver as oneway interface

It used to notify if the window focus is gained or lost, mark it as
oneway to prevent it block the system server when outgoing.

Bug: 238050065
Test: Trigger back gesture and see the logs
Change-Id: I17b79a361edadf03d2b2887cce7ec29c3968e3e5

core/java/android/view/IWindowFocusObserver.aidl

@@ -16,7 +16,7 @@
 package android.view;
 
 /** {@hide} */
-interface IWindowFocusObserver
+oneway interface IWindowFocusObserver
 {
     void focusGained(IBinder inputToken);
     void focusLost(IBinder inputToken);