toCubic method
Converts this segment to a CubicSegment.
This method is used for morphing.
The algrithoms are from https://github.com/thednp/svg-path-commander 2.0.2
Implementation
@override
CubicSegment toCubic(Offset start) {
final controlsRst = lineToCubicControls(start, end);
return CubicSegment(
control1: controlsRst.first,
control2: controlsRst.last,
end: end,
tag: tag,
);
}