Linearly interpolate between two sizes
If either size is null, this function interpolates from Offset.zero.
Source
static Size lerp(Size a, Size b, double t) {
if (a == null && b == null)
return null;
if (a == null)
return b * t;
if (b == null)
return a * (1.0 - t);
return new Size(lerpDouble(a.width, b.width, t), lerpDouble(a.height, b.height, t));
}