HPCC-9848 Optimize fields after resourcing child graphs

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #5209 from ghalliday/issue9848

HPCC-9848 Optimize fields after resourcing child graphs

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>