HPCC-9399 Support smart stepping through a dedup activity

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-9399 Add stepped dedup to hthor and clean up roxie code

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4431 from ghalliday/issue9399a

HPCC-9399 Support smart stepping through a dedup activity

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>