Add proj_query_geodetic_crs_from_datum

[jjimenezshaw]

In the scope of adding a new feature to https://spatialreference.org/ base crs, in a similar way it is done in epsg.org, I think I need proj_query_geodetic_crs_from_datum. (Please, correct me if I am wrong).

The idea will be to get the geographic 3D from a geographic 2D, or a geocentric from a geographic 3D as base crs.

Something like EPSG:6318 -> EPSG:6319 -> EPSG:6317

(For a projected and compound there are already tools in pyproj)

Looking at proj documentation, I think it is doable with proj_query_geodetic_crs_from_datum. It is the only missing piece.

Should I implement that function? Where in the code?

[jjimenezshaw]

cc @rouault

[snowman2]

This would be a good home for it: https://github.com/pyproj4/pyproj/blob/main/pyproj/database.pyx