Allow Herald's "Reviewers" field to select project reviewers

Summary: The "Reviewers" condition in Differential Revision rules has the wrong typeahead and can't select projects, but should be able to.

Test Plan: {F79273}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7526

src/applications/herald/adapter/HeraldAdapter.php

@@ -598,6 +598,8 @@ abstract class HeraldAdapter {
             return self::VALUE_OWNERS_PACKAGE;
           case self::FIELD_AUTHOR_PROJECTS:
             return self::VALUE_PROJECT;
+          case self::FIELD_REVIEWERS:
+            return self::VALUE_USER_OR_PROJECT;
           default:
             return self::VALUE_USER;
         }