Provide "arc look", a user-facing inspection command

Summary:
Ref T13546. Currently, "arc which" provides some amount of inspection but it generally isn't very helpful to users and is too limited and inflexible. "arc inspect" is an internal/debugging workflow.

The new "arc look" is much more aggressively unhelpful.

Test Plan: I'm not sure if this command should allow you to continue at night, because it's too dark.

Maniphest Tasks: T13546

Differential Revision: https://secure.phabricator.com/D21376