Stash transient taskbar upon icon drag

Transient taskbar needs to be stashed upon
dragging the icon from it to create a
splitscreen.

Bug: 258850827

Test: manually reproduced the steps in the bug
Change-Id: I88f2b4b25cb4c12fbe7e646a8ed668921ef24ab9
diff --git a/quickstep/src/com/android/launcher3/taskbar/TaskbarDragController.java b/quickstep/src/com/android/launcher3/taskbar/TaskbarDragController.java
index 3045eca..dfff7ee 100644
--- a/quickstep/src/com/android/launcher3/taskbar/TaskbarDragController.java
+++ b/quickstep/src/com/android/launcher3/taskbar/TaskbarDragController.java
@@ -305,6 +305,9 @@
         if (mDisallowGlobalDrag) {
             AbstractFloatingView.closeAllOpenViewsExcept(mActivity, TYPE_TASKBAR_ALL_APPS);
         } else {
+            // stash the transient taskbar
+            mControllers.taskbarStashController.updateAndAnimateTransientTaskbar(true);
+
             AbstractFloatingView.closeAllOpenViews(mActivity);
         }
 
@@ -413,6 +416,9 @@
                     if (dragEvent.getResult()) {
                         maybeOnDragEnd();
                     } else {
+                        // un-stash the transient taskbar in case drag and drop was canceled
+                        mControllers.taskbarStashController.updateAndAnimateTransientTaskbar(false);
+
                         // This will take care of calling maybeOnDragEnd() after the animation
                         animateGlobalDragViewToOriginalPosition(btv, dragEvent);
                     }