This commit adds signatures to filter refs by visibility to
PermissionBackend.ForProject.
VisibleRefFilter is renamed to DefaultRefFilter and moved into the
permissions package. Minor changes to the class make it fit better into
the new interface structure and make the class easier to read.
Instead of offering config options on the class, this commit adds an
Options AutoValue and forces callers to provide an open repository
handler to the filter method.
Change-Id: I1819de0bab81ed546f1c35461cc5361f1c4027ba
77fd024638