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