Rename `PhutilKeyValueCache` subclasses

Summary: Ref T5655. Depends on D10155.

Test Plan: Ran `arc unit`

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D10156