lerpFrom method
Implementation
@override
Dimension? lerpFrom(Dimension? a, double t) {
if (a == null) return scale(t);
List<Dimension> lengths =
_CompoundDimension.combineLength([a.scale(1 - t), this.scale(t)]);
if (lengths.length == 1) return lengths.first;
return _CompoundDimension(lengths);
}