Rename PhutilKeyValueCache subclasses

Summary: Ref T5655. Rename PhutilKeyValueCache subclasses for consistency. I intentionally left PhutilKeyValueCacheNamespace, PhutilKeyValueCacheProfiler, PhutilKeyValueCacheProxy and PhutilKeyValueCacheStack because these seem to be special cases.

Test Plan: arc lint and arc unit

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D10155