Move PhutilLibraryMapBuilder to libphutil

Summary: See D9813 for a detailed explanation.

Test Plan:

> ./bin/arc liberate
Finding source files...
Found 194 files.
Loading symbol cache...
Found 194 files in cache.
Building library map...
Writing map...
Done.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9815