HPCC-11263 Pack the HqlStmt class, and avoid cloning literals.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #5729 from ghalliday/issue11263

HPCC-11263 Pack the HqlStmt class, and avoid cloning literals.

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>