HPCC-8807 Implement typedefs for dictionary and datasets

Also allow RECORDOF() to work on more argument types.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #3972 from ghalliday/issue8807

HPCC-8807 Implement typedefs for dictionary and datasets

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>