Let root task can reparent to launch root task while launch

When task move to back, we had some mechanism to make sure it is
under task display area or home task parent for legacy split.

For stage split, we should add reparent mechanism when task bring
to front to ensure task is under launch root stage(main stage)
otherwise it will launch as full screen and split dismissed.

Fix: 198554517
Test: manual
Test: pass existing tests
Change-Id: I6ded3d3fa2acc48a8b248b20f6d34b34d5387776

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

@@ -2722,6 +2722,17 @@ class ActivityStarter {
         mTargetRootTask = intentActivity.getRootTask();
         mSupervisor.handleNonResizableTaskIfNeeded(intentTask, WINDOWING_MODE_UNDEFINED,
                 mRootWindowContainer.getDefaultTaskDisplayArea(), mTargetRootTask);
+
+        // We need to check if there is a launch root task in TDA for this target root task.
+        // If it exist, we need to reparent target root task from TDA to launch root task.
+        final TaskDisplayArea tda = mTargetRootTask.getDisplayArea();
+        final Task launchRootTask = tda.getLaunchRootTask(mTargetRootTask.getWindowingMode(),
+                mTargetRootTask.getActivityType(), null /** options */, null /** sourceTask */,
+                0 /** launchFlags */);
+        if (launchRootTask != null && launchRootTask != mTargetRootTask) {
+            mTargetRootTask.reparent(launchRootTask, POSITION_TOP);
+            mTargetRootTask = launchRootTask;
+        }
     }
 
     private void resumeTargetRootTaskIfNeeded() {