upgrade appdied transition trigger to task if relevant

When an app is killed, we send a transition request for it but
with the trigger at activity-level. However, the handleAppDied
logic immediately detaches the Task which means Shell can't
prepare for that (particularly split-screen).

This change will upgrade the trigger to task-level if the task
is going to be removed.

Bug: 251459369
Test: atest EnterSplitScreenFromOverview
Change-Id: Iaf901cb7db41a23a482b67801172053095c8dd47

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

@@ -4076,7 +4076,11 @@ final class ActivityRecord extends WindowToken implements WindowManagerService.A
             // to the restarted activity.
             nowVisible = mVisibleRequested;
         }
-        mTransitionController.requestCloseTransitionIfNeeded(this);
+        // upgrade transition trigger to task if this is the last activity since it means we are
+        // closing the task.
+        final WindowContainer trigger = remove && task != null && task.getChildCount() == 1
+                ? task : this;
+        mTransitionController.requestCloseTransitionIfNeeded(trigger);
         cleanUp(true /* cleanServices */, true /* setState */);
         if (remove) {
             if (mStartingData != null && mVisible && task != null) {