a11y: track item enabled state
disabled items are neither enabled nor focusable
Change-Id: I4f286c7b85605d5ad6fa787d1f5cfcce1297d268 Reviewed-by: Volker Hilsheimer volker.hilsheimer@qt.io Reviewed-by: Jan Arve Sæther jan-arve.saether@qt.io (cherry picked from commit 20fd2902)