Fix scrolling issue in the full widgets picker

Before this change, the widgets recommendation table handles all the
touch events. The table doesn't distinguish a touch event from a scroll
event. This change forwards the motion event to the active recycler view.
If the recycler view doesn't handle the event, it will then forward the
event back to the view hierarchy.

Test: Open the full widgets picker, then start scrolling on the
      recommended widgets UI. The full widgets picker scrolls perfectly.
      Drag-n-drop a recommended widget
Bug: 186567644
Change-Id: I89d473179796c516d2394332dd75f8e9a1d8b388