Un-deprecate CopyableNode, AddedByUsesAware
These traits seem to provide a useful inference summary, related to
DerivableSchemaNode. Un-deprecate them for now to reduce noise for
valid uses which have no alternative.
Also add FIXMEs to reconsider overall design of these interfaces,
as better semantic integration allows for more consistent use.
Change-Id: I3d238f9c6f8d74769506202777efb82277546e63
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit
76943f2ec79511177e9fddc4c2f4a888ccfb0b09)