Implement the GIS function ST_Simplify

The GIS function ST_Simplify takes ad input a geometry (g) and a double (max_distance). It applies the Ramer–Douglas–Peucker algorithm on g and returns the resulting geometry.

The goal of the Douglas-Peucker algorithm is to find a geometry that is similar to g but uses only a subset of points. To perform the simplification, all the vertexes that are shorter than max_distance are removed.

The algorithm may produce self-intersections and therefore result in invalid geometries.

If the max_distance is not positive or is NULL, an ER_WRONG_ARGUMENT will occur.