Do not use prefixOrderIndex for animation layer

We may set a z-order different from the prefix order, for example
TaskDisplayArea#adjustRootTaskLayer. As a result, we should no longer
set animation leash layer based on the prefix order.

Fix: 208793409
Test: manually test launching activity over another
Change-Id: If8d545ca7a9ac42162262ad3a8f95b4ac9f65585

core/java/android/view/RemoteAnimationTarget.java

@@ -129,7 +129,11 @@ public class RemoteAnimationTarget implements Parcelable {
      * The index of the element in the tree in prefix order. This should be used for z-layering
      * to preserve original z-layer order in the hierarchy tree assuming no "boosting" needs to
      * happen.
+     * @deprecated WindowManager may set a z-order different from the prefix order, and has set the
+     *             correct layer for the animation leash already, so this should not be used for
+     *             layer any more.
      */
+    @Deprecated
     @UnsupportedAppUsage
     public final int prefixOrderIndex;
 

packages/SystemUI/animation/src/com/android/systemui/animation/ActivityLaunchAnimator.kt

@@ -436,7 +436,6 @@ class ActivityLaunchAnimator(private val launchAnimator: LaunchAnimator) {
                 .withAlpha(1f)
                 .withMatrix(matrix)
                 .withWindowCrop(windowCrop)
-                .withLayer(window.prefixOrderIndex)
                 .withCornerRadius(cornerRadius)
                 .withVisibility(true)
                 .build()