R1:bce0698a0f5d

Modernize Audit search engine

Summary:
Fixes T9279. Modernizes the SearchEngine and Query classes. User-facing changes:

- Added order by commit date, default to order by commit date with newest commits first.
- Added explicit "Needs Audit by".
- Added new `packages(...)` typeahead function.
- Picked up automatic subscribers, projects, and order fields.

This changes behavior a little bit: we previously attempted to exclude, e.g., commits which a package you own needs to audit, but which you have…