Returns a simple line geometry constructed from the points supplied by the parameters.
Parameter 1 - the start of the line as a simple point geometry.
Parameter 2 - the second vertex of the line as a simple point geometry.
Parameter etc. (optional) - subsequent vertices in the line as simple point geometries.
Returns: a simple line geometry based on the input parameters, or null if not successful.
Note: This function does not fully support 3D geometries. Any 3D geometries will be projected down to 2 dimensions.