In its current state the WidgetPickerActivity only allows adding widget
items, so to match the state, updated it to show only widgets.
manual test - https://screen/cast/NDUxMjg1NjI0MTM0MDQxNnwxMzE4MzNhOS1mZg
Bug: 320495335
Test: atest Launcher3Tests
Flag: N/A
Change-Id: Ifa75f457219efef49e104efc428d369187db2710
The listener allows us to drag and drop widgets outside the launcher.
Bug: 315209740
Test: atest Launcher3Tests
Flag: NA
Change-Id: Iafc6e8903ea4f32540df30152b35d9eb7e98c6d6