hi, thanks for very nice package:)

Is your feature request related to a problem? Please describe
i've just started using fl_chart for line charts in my project and i'm missing an option to add shadow to tooltip:) please check the attached image below

Describe the solution you'd like
i feel like the best solution would be to add some shadow parameters to LineTouchTooltipData

Describe alternatives you've considered
i've tried working-around this effect by playing with available LineTouchTooltipData params but nothing was close to desired effect:)

Additional context