Function smoothstep_derivative 

pub fn smoothstep_derivative<F>(x: F) -> F
where
    F: Copy + From<f32> + Mul<Output = F> + Add<Output = F> + Sub<Output = F>,

Smoothstep derivative for noise with derivatives.

Formula: 30x^2(x-1)^2

Java reference: Mth.smoothstepDerivative(double)