Add InterpolatedRealTransform ?

[bogovicj]

I wrote an InterpolatedRealTransform that is a convex combination two RealTransforms in a spatially varying way.

Given two transforms a and b, it's output (at position x) is:
$$\lambda (x) a(x) + (1 - \lambda(x))b(x)$$
where $\lambda$ controls the "mixture" of a and b in a spatially varying way. It let's you do things like this.

Do we think it's worth moving to this repo? Or is it too niche?