Make herald tokenizers copy values more correctly

Summary:
Fixes T10190. This is still a touch weird (newly typed tokens lose icons when copied) but basically works correctly. Saving/editing rules is fine, just some minor display glitching.

Fixing the icon thing is a little more involved.

Test Plan: Swapped Herald tokenizer fields around saw values (approximately) preserved.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10190

Differential Revision: https://secure.phabricator.com/D15077