private Relationship relationship(Shape shape, RelationshipType type, MemberShape memberShape) {
        return Relationship.create(shape, type, memberShape);
    }
Finds all neighbors of a shape, returning them as a list of
{@link Relationship} objects.

<p>Each neighbor shape that is not in the provided model will
result in a relationship where the optional
{@link Relationship#getNeighborShape() neighbor shape} is empty.

@see NeighborProvider#of
smithy-model/src/main/java/software/amazon/smithy/model/neighbor/NeighborVisitor.java