Border Radius for each corner in BarTouchTooltipData

[cnschnei-btc]

Is your feature request relasted to a problem? Please describe.
My Tooltip for the BarChart should have a custom rounded radius. With the current implementation i can only set a border radius for all 4 corners. I need the bottom left corner not to be rounded (like a speechbubble).

Describe the solution you'd like
It could be implemented that you can provide a normal BorderRadius.