createOperations(): fix issues when transforming between Geog3D and DerivedGeog3D CRS with Geographic3D offsets method

[rouault]

Given test.wkt with:

GEOGCRS["CH1903+ with 10m offset on ellipsoidal height",
    BASEGEOGCRS["CH1903+",
        DATUM["CH1903+",
            ELLIPSOID["Bessel 1841",6377397.155,299.1528128,
                LENGTHUNIT["metre",1]],
            ID["EPSG",6150]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8901]]],
    DERIVINGCONVERSION["Offset on ellipsoidal height",
        METHOD["Geographic3D offsets",
            ID["EPSG",9660]],
        PARAMETER["Latitude offset",0,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8601]],
        PARAMETER["Longitude offset",0,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8602]],
        PARAMETER["Vertical Offset",10,
            LENGTHUNIT["metre",1],
            ID["EPSG",8603]]],
    CS[ellipsoidal,3],
        AXIS["geodetic latitude (Lat)",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433,
                ID["EPSG",9122]]],
        AXIS["geodetic longitude (Lon)",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433,
                ID["EPSG",9122]]],
        AXIS["ellipsoidal height (h)",up,
            ORDER[3],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]]]

$ projinfo -s EPSG:4979 -t @test.wkt --spatial-test intersects -o PROJ --hide-ballpark
Candidate operations found: 1
-------------------------------------
Operation No. 1:

unknown id, Inverse of CH1903+ to WGS 84 (1) + Offset on ellipsoidal height, 1 m, Liechtenstein; Switzerland.

PROJ string:
+proj=pipeline
  +step +proj=axisswap +order=2,1
  +step +proj=unitconvert +xy_in=deg +z_in=m +xy_out=rad +z_out=m
  +step +proj=cart +ellps=WGS84
  +step +proj=helmert +x=-674.374 +y=-15.056 +z=-405.346
  +step +inv +proj=cart +ellps=bessel
  +step +proj=geogoffset +dlat=0 +dlon=0 +dh=10
  +step +proj=unitconvert +xy_in=rad +z_in=m +xy_out=deg +z_out=m
  +step +proj=axisswap +order=2,1

Fixes #3407 (comment)

[hernando]

There's still an issue, it seems the CRS above can't be created programmatically using the C++ API. The factory function DerivedGeographicCRS::create takes a ConversionNNPtr but the coordinate operation "Geographic3D offsets" is a Transformation.