(stable) Make "bin/files" parsing of working set arguments more consistent
Today, basically all of these workflows define their own "--all" and "names" flags. Pull these definitions up and implement them more consistently.
Test Plan: Ran multiple different bin/files commands with different combinations of arguments, saw consistent handling of iterator construction.
Reviewed By: amckinley
Maniphest Tasks: T13326
Differential Revision: https://secure.phabricator.com/D20614