#95641 upgraded Jackson to version 2.15.0.  One of the fixes in this is https://github.com/FasterXML/jackson-core/issues/863.  This new limit of 5000000 characters for a string field then applies to strings in Elasticsearch documents.

To reproduce:

1. `./gradlew run`
2. Download [`big_a.zip`](https://github.com/elastic/elasticsearch/files/11453951/big_a.zip)
3. `unzip big_a.zip`
4. `curl -u elastic:password http://localhost:9200/my-index/_doc/1 -X PUT -d @big_a.json -H 'Content-Type: application/json'`

The response is:

```
{"error":{"root_cause":[{"type":"document_parsing_exception","reason":"[1:20] failed to parse: String length (5043368) exceeds the maximum length (5000000)"}],"type":"document_parsing_exception","reason":"[1:20] failed to parse: String length (5043368) exceeds the maximum length (5000000)","caused_by":{"type":"stream_constraints_exception","reason":"String length (5043368) exceeds the maximum length (5000000)"}},"status":400}
```

I think this is a blocker for release of 8.8.0 because people will have indexed docs in older versions that have strings longer than 5000000 characters, and they won't be able to work with them in 8.8.0 unless we do something about this problem.
libs/x-content/impl/src/main/java/org/elasticsearch/xcontent/provider/json/JsonXContentImpl.java
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */
package org.elasticsearch.xcontent.provider.json;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser;
import org.elasticsearch.xcontent.XContent;
import org.elasticsearch.xcontent.XContentBuilder;
import org.elasticsearch.xcontent.XContentGenerator;
import org.elasticsearch.xcontent.XContentParser;
import org.elasticsearch.xcontent.XContentParserConfiguration;
import org.elasticsearch.xcontent.XContentType;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.Reader;
import java.util.Set;
/**
 * A JSON based content implementation using Jackson.
 */
public class JsonXContentImpl implements XContent {