cubicweb-postgis #3426092 Add support for litteral WKT strings [not validated]

Basically we need to add bindings for ST_GeomFromText() and ST_GeogFromText(). It would then allow writing RQL queries such as

Any Z, ZN
WHERE Z is Zone, Z name ZN, Z type "Commune", Z geometry G
HAVING ST_CONTAINS(G, ST_GEOMFROMTEXT("POINT(651789.5 6862043.0)", 2154)) = TRUE
prioritynormal
typeenhancement
done in0.3.0
load0.500
load left0.000
closed by#eb8c40a52717 Add various GIS functions to RQL functions (closes #3426092)
patchAdd various GIS functions to RQL functions (closes #3426092) [applied]
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