Add custom extra dynamic data for FlSpot

[kylechandev]

Add custom extra dynamic data for FlSpot, then we can easily display the custom information of each data point in LineTouchTooltipData.

For example: FlSpot(double x, double y, dynamic data);

touchTooltipData: LineTouchTooltipData( fitInsideHorizontally: true, fitInsideVertically: true, getTooltipItems: (List<LineBarSpot> touchedBarSpots) { return touchedBarSpots.map((touchedSpot) { dynamic data = touchedSpot.data; } } );

[mluttmann]

Maybe you can get your specific item with touchedSpot.barIndex and touchedSpot.spotIndex.