Build: add infrastructure to build drivers as plugins against an existing libgdal, and apply it to OCI, MrSID and JP2KAK drivers

[rouault]

Inspired from PDAL's STANDALONE mode.

This is a new mode. It is still possible to build those drivers either embedded in libgdal, or as plugins as part of a full GDAL build.

Doc addition for OCI driver:

Standalone plugin compilation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 3.10

While this driver may be built as part of a whole GDAL build, either in libgdal
itself, or as a plugin, it is also possible to only build this driver as a plugin,
against an already built libgdal.

The version of the GDAL sources used to build the driver must match the version
of the libgdal it is built against.

For example, from a "build_oci" directory under the root of the GDAL source tree:

::

    cmake -S ../ogr/ogrsf_frmts/oci -DCMAKE_PREFIX_PATH=/path/to/GDAL_installation_prefix -DOracle_ROOT=/path/to/instantclient_sdk_root
    cmake --build .


Note that such a plugin, when used against a libgdal not aware of it, will be
systematically loaded at GDAL driver initialization time, and will not benefit from
`deferred plugin loading capabilities <rfc-96>`. For that, libgdal itself must be built with the
CMake variable OGR_REGISTER_DRIVER_OCI_FOR_LATER_PLUGIN=ON set.