Don't spend ridiculous amounts of time rebuilding orderable columns

Summary:
Ref T8575. Because orderable columns need to build custom fields, they are relatively expensive to build. Use the request cache.

(The request cache is technically more correct than static, because configuration may change between requests and we may eventually reuse interpreters.)

Test Plan: Saw home page time drop 39% (from 462ms to 283ms).

Reviewers: btrahan, avivey

Reviewed By: avivey

Subscribers: avivey, epriestley

Maniphest Tasks: T8575

Differential Revision: https://secure.phabricator.com/D13322