How to use the @aws-cdk/aws-stepfunctions.Data function in @aws-cdk/aws-stepfunctions

private makePolicyStatements(task: sfn.Task): iam.PolicyStatement[] {
        const stack = Stack.of(task);

        // https://docs.aws.amazon.com/step-functions/latest/dg/sagemaker-iam.html
        const policyStatements = [
            new iam.PolicyStatement({
                actions: ['sagemaker:CreateTrainingJob', 'sagemaker:DescribeTrainingJob', 'sagemaker:StopTrainingJob'],
                resources: [
                    stack.formatArn({
                        service: 'sagemaker',
                        resource: 'training-job',
                        // If the job name comes from input, we cannot target the policy to a particular ARN prefix reliably...
                        resourceName: sfn.Data.isJsonPathString(this.props.trainingJobName) ? '*' : `${this.props.trainingJobName}*`
                    })
                ],
            }),
            new iam.PolicyStatement({
                actions: ['sagemaker:ListTags'],
                resources: ['*']
            }),
            new iam.PolicyStatement({
                actions: ['iam:PassRole'],
                resources: [this._role!.roleArn],
                conditions: {
                    StringEquals: { "iam:PassedToService": "sagemaker.amazonaws.com" }
                }
            })
        ];

(acc, m) => ({
        ...acc,
        [m]: sfn.Data.stringAt(m) // It's okay to always use `stringAt` here
      }),
      {}