Add taskbar stashing feedforward, i.e. hint at upcoming stash/unstash

Also fix unstashing not working in 3P launchers by moving the unstash call from LauncherTaskbarUIController to TaskbarActivityContext

Test: long press taskbar background and stashed handle, watch it hint towards the new stashed/unstashed state respectively and then complete the animation when the long press is triggered
Fixes: 193926311
Fixes: 192926350
Change-Id: I0e538be9129bf5c600d07f360b8106d7077862ad

quickstep/src/com/android/quickstep/TouchInteractionService.java

@@ -680,7 +680,7 @@ public class TouchInteractionService extends Service implements PluginListener<O
             StatefulActivity activity = activityInterface.getCreatedActivity();
             if (activity != null && activity.getDeviceProfile().isTaskbarPresent) {
                 base = new TaskbarStashInputConsumer(this, base, mInputMonitorCompat,
-                        activityInterface);
+                        mTaskbarManager.getCurrentActivityContext());
             }
 
             if (FeatureFlags.ENABLE_QUICK_CAPTURE_GESTURE.get()) {