Adds geom_from_wkb and geom_to_wkb, which mirror the existing
geom_from_wkt/geom_to_wkt functions but for WKB representations
of geometries.
Since QGIS 3.6 we've had good support for binary blob values in
expressions and field values, so adding these functions allows
users to work with binary blob fields containing WKB representations
of geometries (e.g. with a geometry generator showing the encoded
geometries)
