### Elasticsearch Version

8.11+

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

any

### Problem Description

While indexing documents with dynamically added fields, if multiple of those fields are objects are are deeper than 3-5 objects, performance is degraded significantly.

This bug was introduced in: https://github.com/elastic/elasticsearch/pull/90674

### Steps to Reproduce

I built a micro-benchmark to replicate this particular bug. 

But, any dynamic object parsing will cause this.

To mitigate the issue, statically mapped fields for objects is required. 

### Logs (if relevant)

Attached are two JFR files indicating the difference between when the bug was introduce vs. not.
[Archive 2.zip](https://github.com/elastic/elasticsearch/files/13569248/Archive.2.zip)

server/src/main/java/org/elasticsearch/index/mapper/DocumentParserContext.java
@Override
            public boolean isWithinCopyTo() {
                return true;
            }
            @Override
            public LuceneDocument doc() {
                return doc;
            }
        };
    }
    /**
     * Return a context for flattening subobjects
     * @param fieldName   the name of the field to be flattened
     */
    public final DocumentParserContext createFlattenContext(String fieldName) {
        XContentParser flatteningParser = new FlatteningXContentParser(parser(), fieldName);
        return new Wrapper(this.parent(), this) {
            @Override
            public XContentParser parser() {
                return flatteningParser;
            }
        };
    }
    /**
     *  @deprecated we are actively deprecating and removing the ability to pass
     *              complex objects to multifields, so try and avoid using this method
     * Replace the XContentParser used by this context
     * @param parser    the replacement parser
     * @return  a new context with a replaced parser
     */