Rename PhutilBufferedIteratorExample to PhutilExampleBufferedIterator

Summary: Ref T5655. PhutilExampleBufferedIterator seems clearer than PhutilBufferedIteratorExample.

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/D9995