FTransform::AccumulateWithAdditiveScale

Accumulates another transform with this one, with a blending weight

Let SourceAtom = Atom * BlendWeight Rotation is accumulated multiplicatively (Rotation = SourceAtom.Rotation * Rotation). Translation is accumulated additively (Translation += SourceAtom.Translation) Scale3D is accumulated assuming incoming scale is additive scale (Scale3D *= (1 + SourceAtom.Scale3D))

When we create additive, we create additive scale based on [TargetScale/SourceScale -1] because that way when you apply weight of 0.3, you don't shrink. We only saves the % of grow/shrink when we apply that back to it, we add back the 1, so that it goes back to it. This solves issue where you blend two additives with 0.3, you don't come back to 0.6 scale, but 1 scale at the end because [1 + [1-1]*0.3 + [1-1]*0.3] becomes 1, so you don't shrink by applying additive scale

Note: Rotation will not be normalized! Will have to be done manually.