Entry point for C++ Vector API

Since GDAL 3.12, gdal_vector_cpp.h is the include file for all headers related to the C++ Vector API.

In earlier versions, the equivalent is to include gdal_priv.h, ogrsf_frmts.h, ogr_feature.h and ogr_geometry.h

Note that the C++ API is also used by GDAL internals and may be subject from time to time to backwards incompatible changes.