HPCC-8465 Implement THISNODE(dictionary) and serialize to slaves

Also improve the text in error messages for a dictionary

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #3818 from ghalliday/issue8329

HPCC-8465 Implement THISNODE(dictionary) and serialize to slaves

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>