### Environment:
Elasticsearch version:
```
{
    "number" : "7.15.0",
    "build_flavor" : "default",
    "build_type" : "zip",
    "build_hash" : "79d65f6e357953a5b3cbcc5e2c7c21073d89aa29",
    "build_date" : "2021-09-16T03:05:29.143308416Z",
    "build_snapshot" : false,
    "lucene_version" : "8.9.0",
    "minimum_wire_compatibility_version" : "6.8.0",
    "minimum_index_compatibility_version" : "6.0.0-beta1"
}
```
Plugins installed: []
JVM version :1.8
OS version :Windows 10

### Steps to reproduce:
```
PUT test_plain_highlighter 
{}

POST /test_plain_highlighter/_doc/1
{
  "description": [
    "Lorem Ipsum string Generator that helps to create dummy text for all layout needs.",
    "It has roots in a piece of classical Latin literature from 45 BC, making it search string over 2000 years old."
  ]
}

POST /test_plain_highlighter/_search
{
  "highlight": {
    "order": "score",
    "type": "plain",
    "fields": {
      "*": {}
    },
    "fragment_size": 50
  },
  "query": {
    "match": {
      "description": "search string"
    }
  },
  "_source": ""
}
```

### RECEIVED Highlighted Fragment in response:
```
[
   "Lorem Ipsum <em>string</em> Generator that helps to create",
   " literature from 45 BC, making it <em>search</em> <em>string</em> over 2000 years old."
]
```
### EXPECTED Highlighted Fragment:
```
[
   " literature from 45 BC, making it <em>search</em> <em>string</em> over 2000 years old.",
   "Lorem Ipsum <em>string</em> Generator that helps to create"
]
```
server/src/main/java/org/elasticsearch/search/fetch/subphase/highlight/PlainHighlighter.java
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.search.highlight.Encoder;
import org.apache.lucene.search.highlight.Formatter;
import org.apache.lucene.search.highlight.Fragmenter;
import org.apache.lucene.search.highlight.InvalidTokenOffsetsException;
import org.apache.lucene.search.highlight.NullFragmenter;
import org.apache.lucene.search.highlight.QueryScorer;
import org.apache.lucene.search.highlight.SimpleFragmenter;
import org.apache.lucene.search.highlight.SimpleHTMLFormatter;
import org.apache.lucene.search.highlight.SimpleSpanFragmenter;
import org.apache.lucene.search.highlight.TextFragment;
import org.apache.lucene.util.BytesRefHash;
import org.apache.lucene.util.CollectionUtil;
import org.elasticsearch.common.lucene.Lucene;
import org.elasticsearch.common.text.Text;
import org.elasticsearch.index.IndexSettings;
import org.elasticsearch.index.mapper.MappedFieldType;
import org.elasticsearch.search.fetch.FetchContext;
import org.elasticsearch.search.fetch.FetchSubPhase;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import static org.elasticsearch.search.fetch.subphase.highlight.AbstractHighlighterBuilder.MAX_ANALYZED_OFFSET_FIELD;
import static org.elasticsearch.search.fetch.subphase.highlight.UnifiedHighlighter.convertFieldValue;
public class PlainHighlighter implements Highlighter {