R1:8934dee5437b

Add "does not match regexp" to Herald

Summary:
Fixes T10330.

- Anywhere we support "matches regexp", also allow "does not match regexp". Although you can sometimes write a clever negative regexp, these rules are better expressed with "does not match <simple regexp>" anyway, and sometimes no regexp will work.
- Always allow "does not contain" when we support "contains".
- Fix some JS issues with certain rules affecting custom fields.

Test Plan:
- Wrote an "Affected files do not match regexp" rule…