Use getBestURI() to set file handle URIs

Summary: getBestURI() = best URI

Test Plan:
It says "best" in the name so it must be the best!

Also in Maniphest emails we'll link you to /view/ even for binaries and other
non-viewable content.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: anjali, aran

Differential Revision: https://secure.phabricator.com/D1461