Aggregations do not work on a field declared as fast with a parent field is a JSON field with `fast: false`

Minimal reproducible example:

version: 0.6

index_id: test

doc_mapping:
  field_mappings:
    - name: timestamp
      type: datetime
    - name: raw_line
      type: json
      tokenizer: default
      fast: false
    - name: raw_line.statusCode
      type: u64
      fast: true

indexing_settings:
  commit_timeout_secs: 10

Ingest the document:

{"timestamp": 1695934164, "raw_line": {"statusCode": 100, "body": "this is the body"}}

Then execute the term aggregation:

{
  "query": "*",
  "aggs": {
     "my_term": {
        "terms": {
           "field": "raw_line.statusCode"
        }
     }
  }
}

Start by reproducing the issue with the YAML mapping, ingested JSON document, and terms aggregation shown in the report. Trace how the JSON parent field and fast child field are mapped and used by aggregations; done means the raw_line.statusCode terms aggregation returns the indexed value without breaking the parent field configuration.