Since we no longer use a post-validated task in _process_pending_results, we
need to be sure to template fields used in original_task as they are raw and
may contain variables.
This patch also moves the handler tracking to be per-uuid, not per-object.
Doing it per-object had implications for the above due to the fact that the
copy of the original task is now being used, so the only sure way is to track
based on the uuid instead.
Fixes#18289
dd0257b995