[wm]: Move split-secondary stack to front when split-screen is dismissed

In ATMS. Move the split-secondary stack to the front
if the split-screen primary stack shouldn't be focused
after it goes fullscreen.

In AS. If the activity in the primary stack calls moveTaskToBack,
both stacks are dismissed and the launcher is shown.
So move the stack to the bottom
before changing the primary stack to fullscreen stack.

Test: Manual - Exit an app in the split primary stack with the back key,
or drag the divider to the top of the screen.
Test: CtsWindowManagerDeviceTestCases:SplitScreenTests
Bug: 129508970

Change-Id: Ia00fd6ea814b58d59165e860d5390fcfbf1623f6
(cherry picked from commit 19469da7c2053e2c211f73c6da3d25dcaebc3498)
diff --git a/services/core/java/com/android/server/wm/ActivityTaskManagerService.java b/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
index 16dd555..6e3f03d 100644
--- a/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
+++ b/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
@@ -3918,10 +3918,10 @@
                     // Caller wants the current split-screen primary stack to be the top stack after
                     // it goes fullscreen, so move it to the front.
                     stack.moveToFront("dismissSplitScreenMode");
-                } else if (mRootActivityContainer.isTopDisplayFocusedStack(stack)) {
+                } else {
                     // In this case the current split-screen primary stack shouldn't be the top
-                    // stack after it goes fullscreen, but it current has focus, so we move the
-                    // focus to the top-most split-screen secondary stack next to it.
+                    // stack after it goes fullscreen, so we move the focus to the top-most
+                    // split-screen secondary stack next to it.
                     final ActivityStack otherStack = stack.getDisplay().getTopStackInWindowingMode(
                             WINDOWING_MODE_SPLIT_SCREEN_SECONDARY);
                     if (otherStack != null) {