public SummaryTransform bold() {
        return switch (this) {
            case NONE, BOLDED -> BOLDED;
            case DYNAMICBOLDED, DYNAMICTEASER -> DYNAMICBOLDED;
            default -> throw new IllegalArgumentException("Can not bold a '" + this + "' field.");
        };
    }
Returns the bolded version of this transform if possible, throws if not
config-model/src/main/java/com/yahoo/vespa/documentmodel/SummaryTransform.java