A list of values from 0.0 to 1.0 that denote fractions along the gradient.
If non-null, this list must have the same length as colors.
If the first value is not 0.0, then a stop with position 0.0 and a color equal to the first color in colors is implied.
If the last value is not 1.0, then a stop with position 1.0 and a color equal to the last color in colors is implied.
The values in the stops list must be in ascending order. If a value in the stops list is less than an earlier value in the list, then its value is assumed to equal the previous value.
If stops is null, then a set of uniformly distributed stops is implied, with the first stop at 0.0 and the last stop at 1.0.
final List<double>? stops;