GPKG: map Null CRS to a new srs_id=99999, and add a SRID layer creation option

[rouault]

New layer creation option:

-  .. lco:: SRID
      :choices: <integer>
      :since: 3.9

      Forced ``srs_id`` of the entry in the ``gpkg_spatial_ref_sys`` table to point to.
      This may be -1 ("Undefined Cartesian SRS"), 0 ("Undefined geographic SRS"),
      99999 ("Undefined SRS"), a valid EPSG CRS code or an existing entry of the
      ``gpkg_spatial_ref_sys`` table. If pointing to a non-existing entry, only a warning
      will be emitted.

Coordinate Reference Systems
----------------------------

Starting with GDAL 3.9, a layer without any explicit CRS is mapped from/to a
custom entry of srs_id=99999 with the following properties:

- ``srs_name``: ``Undefined SRS``
- ``organization``: ``GDAL``
- ``organization_coordsys_id``: 99999
- ``definition``: ``LOCAL_CS["Undefined SRS",LOCAL_DATUM["unknown",32767],UNIT["unknown",0],AXIS["Easting",EAST],AXIS["Northing",NORTH]]``
- ``definition_12_063`` (when the CRS WKT extension is used): ``ENGCRS["Undefined SRS",EDATUM["unknown"],CS[Cartesian,2],AXIS["easting",east,ORDER[1],LENGTHUNIT["unknown",0]],AXIS["northing",north,ORDER[2],LENGTHUNIT["unknown",0]]]``
- ``description``: ``Custom undefined coordinate reference system``

Note that the use of a LOCAL_CS / EngineeringCRS is mostly to provide a valid
CRS definition to comply with the requirements of the GeoPackage specification
and to be compatible of other applications (or GDAL 3.8 or earlier), but the
semantics of that entry is intented to be "undefined SRS of any kind".

[jratike80]

Is it good to use different srs_id=99999 and organization_coordsys_id=0? There may be a slight possibility for a mess because geopackage developers can think that those two are always equal, because usually for the EPSG codes they are. But if someone cares about the organization then hopefully they check correctly the combination organization + organization_coordsys_id and notice that NONE:0 is not the same than GDAL:0.
(Well, I think I wouldn't care about that difference myself, and at least not between NONE:-1 and GDAL:0)

Maybe the definition could somehow distinct the new undefined from the two existing undefined variants. Something like "Custom undefined coordinate reference system". Or "Undefined coordinate reference system using undefined units". This suggestion does not feel most clear.

0 (NONE 0) = undefined Cartesian coordinate reference system
-1 (NONE -1) = undefined geographic coordinate reference system
99999 (GDAL 0) = undefined coordinate reference system

Was there someone who wished to have undefined undefined Cartesian and undefined undefined non-Cartesian?

[rouault]

Is it good to use different srs_id=99999 and organization_coordsys_id=0?

ok, I've change organization_coordsys_id to 99999 as well

Something like "Custom undefined coordinate reference system"

I've changed to that

[rouault]

Fixes #9580