Shift RoundedCornerOverlay to Display window hierarchy

ScreenDecorations use rounded corner overlay flag and are
currently drawn outside of the window hierarchy,
It currently blocking touches to the gesture monitor spy
windows. By bringing them to Display content Surface control,
we make them in the same tree as the gesture monitor. And
since gesture monitor window are hugher in z ordering they
will take precedence for touch events over ScreenDecorations.

Test: manual

Bug: 225505986
Change-Id: If60450c5e6f29c23a96ce8a89a5ba7d47ee8609d

services/core/java/com/android/server/wm/WindowToken.java

@@ -379,7 +379,7 @@ class WindowToken extends WindowContainer<WindowState> {
     SurfaceControl.Builder makeSurface() {
         final SurfaceControl.Builder builder = super.makeSurface();
         if (mRoundedCornerOverlay) {
-            builder.setParent(null);
+            builder.setParent(getDisplayContent().getSurfaceControl());
         }
         return builder;
     }