Rename "HeraldAction" to "HeraldActionRecord"

Summary:
Ref T8726. I want to modularize actions like fields, but the base class should be "HeraldAction".

Eventually, "HeraldCondition" should probably be "HeraldFieldRecord", and then both Action and Condition should just be rolled into Rule, probably, but that can wait and doesn't block anything.

Test Plan: Ran migration, poked around UI, used git grep.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8726

Differential Revision: https://secure.phabricator.com/D13644