Create a description for variable edge easing using either normalised or physical lengths.

Input parameters:

1. Ex → Index of edge these radii pertain to.
2. Rd → List of easing radii. One for each length marker.
3. Ln → List of length markers. One for each radius.
4. Nr → If true, the length markers are considered normalised; 0.0=start and 1.0=end. If false, the lengths are interpreted as physical lengths along the edge, with negative lengths indicating backwards motion from the end of the curve.

Output parameters:

1. Ed → Variable edge easing descriptor to be used in the 'Ease Edges' component.