[TOptional](API\Runtime\Core\IO\TOptional)< [FPlacementModeID](API\Editor\PlacementMode\FPlacementModeID) > RegisterPlaceableItem ( [FName](API\Runtime\Core\UObject\FName) CategoryName, const [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [FPlaceableItem](API\Editor\PlacementMode\FPlaceableItem) > & Item )