[ Version ( since = "1.4" ) ]
public DragAction extra_drag_preferred_action { get; }
The unique action on the `current-drop` of the [signal@TabBar:AdapTabBar:extra-drag-drop].
This property should only be used during a [signal@TabBar:AdapTabBar:extra-drag-drop] and is always a subset of what was
originally passed to [method@TabBar.setup_extra_drop_target].