HPCC-11561 Allow DEDUP and ROLLUP to include (child) rows as expressions

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6033 from ghalliday/issue11561

HPCC-11561 Allow DEDUP and ROLLUP to include (child) rows as expressions

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>