HPCC-10424 Make codegen use of IXmlWriter JSON compatible

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #5143 from afishbeck/eclgen_json_array

HPCC-10424 Make codegen use of IXmlWriter JSON compatible

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>