Avoid flicker to drop a widget that needs a config activity.

When dropping a widget that requires an config activity, drop a
PendingAppWidgetHostView to workspace

Adb command to try the feature:

adb shell device_config put launcher com.android.launcher3.enable_add_app_widget_via_config_activity_v2 true

Fix: 284236964
Test: manual
Flag: aconfig launcher.enable_add_app_widget_via_config_activity_v2 DISABLED
Change-Id: Ifd0be5c607a388cf8a8f6d77b46c03112e3e599f

src/com/android/launcher3/Workspace.java

@@ -2988,7 +2988,7 @@ public class Workspace<T extends View & PageIndicator> extends PagedView<T>
     }
 
     public void animateWidgetDrop(ItemInfo info, CellLayout cellLayout, final DragView dragView,
-            final Runnable onCompleteRunnable, int animationType, final View finalView,
+            final Runnable onCompleteRunnable, int animationType, @Nullable final View finalView,
             boolean external) {
         int[] finalPos = new int[2];
         float scaleXY[] = new float[2];