highlightShape property Null safety
The shape (e.g., circle, rectangle) to use for the highlight drawn around this part of the material when pressed, hovered over, or focused.
If the shape is BoxShape.circle, then the highlight is centered on the InkResponse. If the shape is BoxShape.rectangle, then the highlight fills the InkResponse, or the rectangle provided by getRectCallback if the callback is specified.
final BoxShape highlightShape;