Add Displaycontent Detection

The root cause is moveTaskToBackInner may start at a later time,
should ensure that the task is still attached before calling moveTaskToBackInner.

Bug: 273689553
Test: run monkey test
Change-Id: I606eb22df1f6b36b478a1f3db51d73657a766a0d

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

@@ -5652,7 +5652,7 @@ class Task extends TaskFragment {
                     (deferred) -> {
                         // Need to check again if deferred since the system might
                         // be in a different state.
-                        if (deferred && !canMoveTaskToBack(tr)) {
+                        if (!isAttached() || (deferred && !canMoveTaskToBack(tr))) {
                             Slog.e(TAG, "Failed to move task to back after saying we could: "
                                     + tr.mTaskId);
                             transition.abort();