Support alt+tab for desktop tasks

Updates keyboard quickswitch logic handle quickswitching while on
desktop. When on desktop, alt+tab moves only between desktop tasks.
Fullscreen tasks are shown in the overflow tile and can be accessed by
going to overview.

TODO:
- when not in desktop and using quickswitch, show the desktop tile as a
  combined tile in the row, similar to what is shown in overview

Flag: persist.wm.debug.desktop_mode_2
Bug: 280468885
Test: open some apps on desktop and have some fullscreen apps opened in
  the background, when on desktop, observe that alt+tab only switches
  between desktop tasks
Test: same setup, but switch to a fullscreen app, observe that alt+tab
  only switches between fullscreen tasks and desktop is accessible from
  overview

Change-Id: Ib19f2eaa24363bbd0669c8c8c3d99ed9d9118a17

quickstep/src/com/android/launcher3/taskbar/KeyboardQuickSwitchViewController.java

@@ -27,6 +27,7 @@ import androidx.annotation.Nullable;
 import com.android.launcher3.anim.AnimationSuccessListener;
 import com.android.launcher3.taskbar.overlay.TaskbarOverlayContext;
 import com.android.launcher3.taskbar.overlay.TaskbarOverlayDragLayer;
+import com.android.quickstep.SystemUiProxy;
 import com.android.quickstep.util.GroupTask;
 import com.android.systemui.shared.recents.model.Task;
 import com.android.systemui.shared.recents.model.ThumbnailData;
@@ -52,6 +53,8 @@ public class KeyboardQuickSwitchViewController {
 
     private int mCurrentFocusIndex = -1;
 
+    private boolean mOnDesktop;
+
     protected KeyboardQuickSwitchViewController(
             @NonNull TaskbarControllers controllers,
             @NonNull TaskbarOverlayContext overlayContext,
@@ -71,10 +74,12 @@ public class KeyboardQuickSwitchViewController {
             @NonNull List<GroupTask> tasks,
             int numHiddenTasks,
             boolean updateTasks,
-            int currentFocusIndexOverride) {
+            int currentFocusIndexOverride,
+            boolean onDesktop) {
         TaskbarOverlayDragLayer dragLayer = mOverlayContext.getDragLayer();
         dragLayer.addView(mKeyboardQuickSwitchView);
         dragLayer.runOnClickOnce(v -> closeQuickSwitchView(true));
+        mOnDesktop = onDesktop;
 
         mKeyboardQuickSwitchView.applyLoadPlan(
                 mOverlayContext,
@@ -136,6 +141,10 @@ public class KeyboardQuickSwitchViewController {
         GroupTask task = mControllerCallbacks.getTaskAt(index);
         if (task == null) {
             return Math.max(0, index);
+        } else if (mOnDesktop) {
+            UI_HELPER_EXECUTOR.execute(() ->
+                    SystemUiProxy.INSTANCE.get(mKeyboardQuickSwitchView.getContext())
+                            .showDesktopApp(task.task1.key.id));
         } else if (task.task2 == null) {
             UI_HELPER_EXECUTOR.execute(() ->
                     ActivityManagerWrapper.getInstance().startActivityFromRecents(