ProjectRepairer: Add a --copy-loose-objects repair action

Add a COPY_LOOSE_OBJECTS action, exposed as '--copy-loose-objects',
rsyncing the two hex character fanout directories under objects/. The
include patterns keep rsync out of pack/, info/ and their siblings.

The action is declared ahead of COPY_PACKS, so when both are selected
loose objects are copied first. '--full' now covers both.

Change-Id: I9c3d12182bdc5fa9da662269d8681db174057f21