Attach the RB.DiffFile to RB.DiffReviewable as an attribute.
Review Request #9165 — Created Aug. 31, 2017 and submitted
RB.DiffReviewableinstances are built based on a
some of the attributes from the file end up in the reviewable. Some
upcoming code needs access to more of the file's attributes, so instead
of plumbing all those in, we now attach the file to the reviewable as an
fileIndexattribute on the reviewable has been removed.
Callers now access this from the associated file.
Unit tests pass.
Manually tested navigating between revisions, pages, and file anchors
using the index.