Implement the GIS function ST_Collect

The GIS function ST_Collect takes as input multiple geometries and returns the aggregation of the distinct geometry arguments.
This function also supports the DISTINCT option. If the DISTINCT case is used, it returns the aggregation of the distinct geometry arguments.

The resulting value type is choosen using the following policy:

• If all arguments are Point values, the result is a MultiPoint value.
• If all arguments are LineString values, the result is a MultiLineString value.
• If all arguments are Polygon values, the result is a MultiPolygon value.
• Otherwise, the result is a GeometryCollection value.

If there are multiple geometry arguments and those arguments are in the same SRS, the return value is in that SRS. If those arguments are not in the same SRS, an ER_GIS_DIFFERENT_SRIDS_AGGREGATION error occurs.