private Pair<ShapeId, ShapeId> applyServiceRenames(ShapeId fromId, ShapeId toId, ServiceShape service) {
        if (service.getRename().containsKey(fromId)) {
            ShapeId newId = ShapeId.fromParts(toId.getNamespace(), service.getRename().get(fromId));
            return Pair.of(fromId, newId);
        }
        return Pair.of(fromId, toId);
    }
Gets the set of tags that are retained in the model.

@return Returns the tags to retain.
smithy-build/src/main/java/software/amazon/smithy/build/transforms/FlattenNamespaces.java