Merge redundant Herald effect code

Summary: Ref T7849. Lift more action handling out of adapters. In theory, adapters will some day do no action handling. That day is not today, but it is now a step closer.

Test Plan:

• Wrote a rule using the email and flag actions.
• Ran that rule.
• Got an email and flag.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7849

Differential Revision: https://secure.phabricator.com/D12502