fix(stepfunctions): support json path fields for item batcher

The ItemBatcher property of DistributedMap supports json path fields,
but the new DistributedMap construct doesn't call
FieldUtils.renderObject when rendering the ItemBatcher.

Make sure to call `FieldUtils.renderObject()` when rendering this
property.

Added an integration test to ensure that the json path field resolves to
the actual value from the state in the input by checking the output from
the results writer in S3.

packages/@aws-cdk-testing/framework-integ/test/aws-stepfunctions/test/integ-assets/get-succeeded-batch-execution-result/index.ts

@@ -0,0 +1,61 @@
+/* eslint-disable no-console */
+
+import {
+  S3Client,
+  ListObjectsV2Command,
+  GetObjectCommand,
+} from '@aws-sdk/client-s3';
+
+const client = new S3Client({});
+
+type ResultObject ={
+  ExecutionArn: string;
+  Input: string;
+  InputDetails: { Included: boolean };
+  Name: string;
+  Output: string;
+  OutputDetails: { Included: boolean };
+  RedriveCount: number;
+  RedriveStatus: string;
+  RedriveStatusReason: string;
+  StartDate: string;
+  StateMachineArn: string;
+  Status: string;
+  StopDate: string;
+};
+
+export async function handler(event: { bucket: string; prefix: string }) {
+  console.log('handling event', event);
+
+  console.log('getting key for results writer succeeded file');
+  const listObjectsCommandOutput = await client.send(new ListObjectsV2Command({
+    Bucket: event.bucket,
+    Prefix: event.prefix,
+  }));
+
+  if (!listObjectsCommandOutput.Contents) {
+    throw new Error('No objects found');
+  }
+
+  const succeedKey = listObjectsCommandOutput.Contents.find((object) => object?.Key?.endsWith('SUCCEEDED_0.json'));
+
+  if (!succeedKey) {
+    throw new Error('No SUCCEEDED_0.json found');
+  }
+  console.log('found key', succeedKey.Key);
+
+  console.log('getting object');
+  const object = await client.send(new GetObjectCommand({
+    Bucket: event.bucket,
+    Key: succeedKey.Key,
+  }));
+
+  if (!object?.Body) {
+    throw new Error('No object body found');
+  }
+
+  const body: ResultObject[] = JSON.parse(await object.Body.transformToString());
+  console.log('got succeeded object body', body);
+
+  return JSON.parse(body[0].Input);
+}