Make Herald conditions and actions more resilient (see discussion in D12896). This protects against invalid rules, which may have been valid in the past but are no longer valid. Specifically:
- If a rule has an invalid field, the conditions fail and the actions do not execute.
- The transcript shows that the rule failed because of an invalid field, and points at the issue.
- If a rule has an invalid action, that action fails but other actions execute.
- The transcript shows that the action failed.
- Everything else (particularly, other rules) continues normally in both cases.
- The edit interface is somewhat working when editing an invalid rule, but it could use some further improvements.