Update "arc land" display of build failures, and rename "DisplayRef" to "RefView"
Ref T13546. Show ongoing and failed builds more clearly in "arc land" output.
Also rename "DisplayRef" (which is not a "Ref") to "RefView" with the goal of improving clarity, and let callers "build...()" it so they can add more status, etc., information.
Get rid of "[DisplayRef|RefView]Interface". In theory, future refs (say, in Phabricator) might not do anything here, but every Ref just ends up implementing it. This could perhaps be subclassed more narrowly in the future if necessary.
Test Plan: Ran "arc land", grepped for various symbols.
Maniphest Tasks: T13546
Differential Revision: https://secure.phabricator.com/D21352