New Pipeline: Call SectionHeaderView.isContentVisible=true when added.

This was called by NotificationSectionsManager in the old pipeline, whenever that manager added the view.
I added a hook to the new pipeline's NodeController interface and had SectionHeaderController call it there.

Fixes: 211161592
Test: manual testing with the repro steps
Change-Id: Ie7f10ac584b79c9e656e1f5d5cbf1f974a57c57f