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