HPCC-8490 Can't convert dictionary to dataset in output spec

Add support for listing a dictionary field in a record def for output.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #3985 from richardkchapman/dict-output2

HPCC-8490 Can't convert dictionary to dataset in output spec

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>