R1:f5c9b9c014a7

Make Herald rules more resilient

Summary:
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 This protects against invalid rules, which may have been valid in the past but are no longer valid.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.