Mirror "secure" content

Some applications, like Silence, prevent the content of a window from
being viewed on non-secure displays:
<https://developer.android.com/reference/android/view/WindowManager.LayoutParams.html#FLAG_SECURE>

We can mirror it by just creating a "secure" display:
<https://developer.android.com/reference/android/view/Display#FLAG_SECURE>

server/src/main/java/com/genymobile/scrcpy/ScreenEncoder.java

@@ -151,7 +151,7 @@ public class ScreenEncoder implements Device.RotationListener {
     }
 
     private static IBinder createDisplay() {
-        return SurfaceControl.createDisplay("scrcpy", false);
+        return SurfaceControl.createDisplay("scrcpy", true);
     }
 
     private static void configure(MediaCodec codec, MediaFormat format) {