Add a detection method of the geometry types actually in a file for a "Geometry" geometrycolumn

[theroggy]

Some files have a column defined as "Geometry", but actually have only one primitive type in them (e.g. multi + single polygons) in them and so could still get proper automatic treatment in geo operations.

For this type of files an automatic detection would be useful...

• make a function to determine all geometry types in a layer (geofileops.get_layer_geometrytypes)
• use function to automatically deal with this if possible in all geo operations
• A special case of this is geofiles that don't contain any rows and have a geometry column of type "Geometry". For this situation the geometrytype is not important at all for any spatial operations.

[theroggy]

A distinct ST_GeometryType(geom) should do the trick