Make taskbar visibilty change only in desktop.

Make the DesktopVisibilityController not change the taskbar visibility
when there are no freeform tasks visible.

Test: Go from freeform to fullscreen, observe taskbar doesn't pop up
Bug: 323129412
Flag: ACONFIG com.android.wm.shell.enable_desktop_windowing DEVELOPMENT
Change-Id: I67f246cfc2ddc198326c093fd0af83886de8b0a9

quickstep/src/com/android/launcher3/statehandlers/DesktopVisibilityController.java

@@ -285,7 +285,8 @@ public class DesktopVisibilityController {
         if (dragLayer != null) {
             dragLayer.setVisibility(visibility);
         }
-        if (mLauncher instanceof QuickstepLauncher ql && ql.getTaskbarUIController() != null) {
+        if (mLauncher instanceof QuickstepLauncher ql && ql.getTaskbarUIController() != null
+                && mVisibleFreeformTasksCount != 0) {
             ql.getTaskbarUIController().onLauncherVisibilityChanged(visibility == VISIBLE);
         }
     }