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 touchedBarSpots) {
return touchedBarSpots.map((touchedSpot) {
dynamic data = touchedSpot.data;
}
}
);

[mluttmann]

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