Don't no-op on resuming top activity if display is in freeform.

Currently, when we try to resume the top activity of the task, we exit
early if the activity is already resumed. However in the case of
freeform display area and multi-resume, it's possible we want to
proceed with the rest of the operation (pausing the back stack based on
visibility check) since multi-resume is possible. For example, in the
case of a maximized app behind a freeform app, when we bring the
maximized, fullscreen app to the front (which is already resumed), we
want to then pause the back stacks since everything is covered up.

Bug: 168852384
Test: atest
PinnedStackTests#testAutoEnterPictureInPictureOnUserLeaveHintWhenPipRequestedNotOverridden

Change-Id: If2dc3f97ca2afd2992c7546e91a36d826cbf9c72

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

@@ -5870,7 +5870,11 @@ class Task extends WindowContainer<WindowContainer> {
         final TaskDisplayArea taskDisplayArea = getDisplayArea();
 
         // If the top activity is the resumed one, nothing to do.
+        // For devices that are not in fullscreen mode (e.g. freeform windows), it's possible
+        // we still want to proceed if the visibility of other windows have changed (e.g. bringing
+        // a fullscreen window forward to cover another freeform activity.)
         if (mResumedActivity == next && next.isState(RESUMED)
+                && taskDisplayArea.getWindowingMode() != WINDOWING_MODE_FREEFORM
                 && taskDisplayArea.allResumedActivitiesComplete()) {
             // Make sure we have executed any pending transitions, since there
             // should be nothing left to do at this point.