lerp static method
Linearly interpolate between two EdgeInstes
Implementation
static EdgeInsets? lerp(EdgeInsets? a, EdgeInsets? 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 EdgeInsets.fromLTRB(
    _lerpDouble(a.left, b.left, t),
    _lerpDouble(a.top, b.top, t),
    _lerpDouble(a.right, b.right, t),
    _lerpDouble(a.bottom, b.bottom, t),
  );
}