HPCC-9401 Update based on review and missing changes

Removed IPropTree::getIsArrayItem().  toJSON now looks ahead one child
item to determine when an element repeats.

Also reimplemented lost changes to only create a workunit if/when its
actually needed.

Also fixed various other items caught in code review.

 to delay creating workunit

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>