GPKG: Support aspatial tables via the gdal_aspatial extension.

See geopackage_aspatial.html for the specification. Fixes #5521

git-svn-id: https://svn.osgeo.org/gdal/trunk@27463 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx