GPKG: emit warning when required extensions are not implemented

git-svn-id: https://svn.osgeo.org/gdal/trunk@27350 f0d54148-0727-0410-94bb-9a71ac55c965
GPKG: Test a bit more optimizations of ExecuteSQL()

git-svn-id: https://svn.osgeo.org/gdal/trunk@27351 f0d54148-0727-0410-94bb-9a71ac55c965