### Elasticsearch Version

8.6.2

### Installed Plugins

mapper-size

### Java Version

_bundled_

### OS Version

3.10.0-1160.83.1.el7.x86_64

### Problem Description

Elastic mapper-size plugin fails on version 8.6.2 with updated templates for global, index, and component (both custom and managed).  It does work in 8.5.0

### Steps to Reproduce

Enable plugin, enable _size field, ingest data
![image](https://user-images.githubusercontent.com/11168913/224350960-498d5abd-62f5-4564-9f62-ac0702c2dd20.png)
![image](https://user-images.githubusercontent.com/11168913/224351072-977a4d34-68cb-448b-9fc3-86f223171de9.png)
![image](https://user-images.githubusercontent.com/11168913/224351165-e5ee1a54-216f-4b20-a571-a09ece65274c.png)
![image](https://user-images.githubusercontent.com/11168913/224351286-13593e3a-d9a2-4b47-ad3c-fa55ea63f4f5.png)

**Works in 8.5.0 though!**
![image](https://user-images.githubusercontent.com/11168913/224351648-5184f1df-0579-4d53-a7a1-97230570a1d5.png)



### Logs (if relevant)

_No response_
plugins/mapper-size/src/main/java/org/elasticsearch/index/mapper/size/SizeFieldMapper.java
private SizeFieldMapper(Explicit<Boolean> enabled, MappedFieldType mappedFieldType) {
        super(mappedFieldType);
        this.enabled = enabled;
    }
    @Override
    protected String contentType() {
        return NAME;
    }
    public boolean enabled() {
        return this.enabled.value();
    }
    @Override
    public void postParse(DocumentParserContext context) {
        
        if (enabled.value() == false) {
            return;
        }
        final int value = context.sourceToParse().source().length();
        NumberType.INTEGER.addFields(context.doc(), name(), value, true, true, true);
    }
    @Override
    public FieldMapper.Builder getMergeBuilder() {
        return new Builder().init(this);
    }
    @Override
    public SourceLoader.SyntheticFieldLoader syntheticFieldLoader() {
        return SourceLoader.SyntheticFieldLoader.NOTHING;
    }
}