DataLabelTapCallback typedef
        DataLabelTapCallback =
     void Function(DataLabelTapDetails onTapArgs)
    
    
typedef common for all the chart types
Signature for callback reporting that a data label is tapped.
Also refer onDataLabelTapped event and DataLabelTapDetails class.
Implementation
typedef DataLabelTapCallback = void Function(DataLabelTapDetails onTapArgs);