navigation
The navigation (up / back) icon at the toolbar's leading edge, or ToolbarIcon.None (the default) for no navigation affordance. Tapping it dispatches ToolbarAction.NavigationClicked. Set via com.pspdfkit.compose.toolbar.adapter.ToolbarCoordinator.setMainToolbarNavigationIcon.
Not part of the saved snapshot: like the items, the host re-supplies it on restore.