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