Limit launching placeholder to top TaskFragment

Currently, we launch placeholder Activity if Activity is not split
and matches placeholder rule. However, there's a scenario that
the Activity which matches placeholder rule is occulded by a fullscreen
Activity, but SplitController still launches placeholder on top of the
fullscreen Activity.

This CL verifies if the Activity located TaskFragmentContainer is on top
to launch placeholder. It also makes #getTopActiveContainer consider
Activity from other process by verifying #getRunningActivityCount.

Test: manual - Repro steps in bugs
Bug: 214175523

Change-Id: Id287d8c5235918b78ccd43bfddf9bb17ee0ff2e8

libs/WindowManager/Jetpack/src/androidx/window/extensions/embedding/SplitController.java

@@ -404,7 +404,7 @@ public class SplitController implements JetpackTaskFragmentOrganizer.TaskFragmen
     TaskFragmentContainer getTopActiveContainer() {
         for (int i = mContainers.size() - 1; i >= 0; i--) {
             TaskFragmentContainer container = mContainers.get(i);
-            if (!container.isFinished() && container.getTopNonFinishingActivity() != null) {
+            if (!container.isFinished() && container.getRunningActivityCount() > 0) {
                 return container;
             }
         }
@@ -499,6 +499,10 @@ public class SplitController implements JetpackTaskFragmentOrganizer.TaskFragmen
     boolean launchPlaceholderIfNecessary(@NonNull Activity activity) {
         final  TaskFragmentContainer container = getContainerWithActivity(
                 activity.getActivityToken());
+        // Don't launch placeholder if the container is occluded.
+        if (container != getTopActiveContainer()) {
+            return false;
+        }
 
         SplitContainer splitContainer = container != null ? getActiveSplitForContainer(container)
                 : null;