Extend the OGR C Interface `OGR_F_StealGeometry` function to geometries other than 1st one

[mathieu17g]

Would there be any undesirable side effects of implementing OGR_F_StealGeometry( int iGeomField ) as it is available as a C++ method but not on the C interface ?

The need relates to ArchGDAL.jl when converting a OGR Feature Layer to a table object. Stealing geometries is faster than cloning. This would bring a performance enhancement for layers with multiple geometry fields (yeesian/ArchGDAL.jl#266)

[rouault]

Would there be any undesirable side effects of implementing OGR_F_StealGeometry( int iGeomField ) as it is available as a C++ method but not on the C interface ?

would be reasonable, as a new function OGRGeometryH CPL_DLL OGR_F_StealGeometryEx( OGRFeatureH, int iGeomField ) CPL_WARN_UNUSED_RESULT .
Are you willing to do a pull request for that ?

[mathieu17g]

Sure I can give a try
I can read C/C++ but have not written any code in C/C++ since the nineties :-)

[mathieu17g]

@rouault I have made a PR (my first PR in C/C++ actually).
But I need some guidance to complete the PR #5196 .

Testing:

• I haven't found any unit testing using OGR_F_StealGeometry and therefore have no clue where to put unit testing if required
• I do have found OGR_F_StealGeometry usage in other functions for which I have not found anything looking like testing
  I must miss something about testing of compiled languages. Could you give me an hint where to look for ?

Documentation: I have updated documentation comment blocks in the relevant source file. Is there any other documentation source to update ?