public Builder addShapeLink(ShapeId id, ShapeLink link) {
            List<ShapeLink> list = this.shapes.getOrDefault(id, new ArrayList<>());
            list.add(link);
            this.shapes.put(id, list);
            return this;
        }
Adds a ShapeLink to this ShapeId in the TraceFile's shapes map.

@param id   ShapeId
@param link ShapeLink corresponding to ShapeId
@return This builder.
smithy-codegen-core/src/main/java/software/amazon/smithy/codegen/core/trace/TraceFile.java