Apply Chaikin's algorithm to a polyline a given number of times.

Input parameters:

1. Pl → Base polyline to subdivide.
2. It → Number of subdivision iterations to apply. Each iteration roughly doubles the number of vertices.
3. S1 → Parameter along each segment where the first subdivision occurs, as a normalised number.
4. S2 → Parameter along each segment where the second subdivision occurs, as a normalised number.

Output parameters:

1. Pl → Subdivided polyline representing the intermediate Chaikin curve.