If tsdb is enabled and the mapping contains fields of type `match_only_text` then these fields are not visible in the _source
in the search response.

Reproduction of this issue:

```

PUT _index_template/my-weather-sensor-index-template
{
    "index_patterns": [
        "metrics-weather_sensors-*"
    ],
    "data_stream": {},
    "template": {
        "settings": {
            "index.mode": "time_series",
            "index.routing_path": [
                "sensor_id",
                "location"
            ],
            "index.look_ahead_time": "3h"
        },
        "mappings": {
            "properties": {
                "sensor_id": {
                    "type": "keyword",
                    "time_series_dimension": true
                },
                "location": {
                    "type": "keyword",
                    "time_series_dimension": true
                },
                "temperature": {
                    "type": "half_float",
                    "time_series_metric": "gauge"
                },
                "humidity": {
                    "type": "half_float",
                    "time_series_metric": "gauge"
                },
                "@timestamp": {
                    "type": "date",
                    "format": "strict_date_optional_time"
                },
                "message": {
                    "type": "match_only_text"
                }
            }
        }
    },
    "priority": 500,
    "_meta": {
        "description": "Template for my weather sensor data"
    }
}

DELETE _data_stream/metrics-weather_sensors-dev

POST /metrics-weather_sensors-dev/_doc
{
    "@timestamp": "2023-07-04T11:21:15.000Z",
    "sensor_id": "HAL-000001",
    "location": "plains",
    "temperature": 26.7,
    "humidity": 49.9,
    "message": "hey"
}

POST /metrics-weather_sensors-dev/_doc
{
    "@timestamp": "2023-07-04T11:25:42.000Z",
    "sensor_id": "SYKENET-000001",
    "location": "swamp",
    "temperature": 32.4,
    "humidity": 88.9,
    "message": "you"
}

GET /metrics-weather_sensors-dev/_search
```

The search response will not contain the `message` field in the `_source` and this field should exist.
server/src/main/java/org/elasticsearch/index/IndexMode.java
/**
     * Get default mapping for this index or {@code null} if there is none.
     */
    @Nullable
    public abstract CompressedXContent getDefaultMapping();
    /**
     * Build the {@link FieldMapper} for {@code _id}.
     */
    public abstract IdFieldMapper buildIdFieldMapper(BooleanSupplier fieldDataEnabled);
    /**
     * Get the singleton {@link FieldMapper} for {@code _id}. It can never support
     * field data.
     */
    public abstract IdFieldMapper idFieldMapperWithoutFieldData();
    /**
     * @return the time range based on the provided index metadata and index mode implementation.
     *         Otherwise <code>null</code> is returned.
     */
    @Nullable
    public abstract TimestampBounds getTimestampBound(IndexMetadata indexMetadata);
    /**
     * Return an instance of the {@link TimeSeriesIdFieldMapper} that generates
     * the _tsid field. The field mapper will be added to the list of the metadata
     * field mappers for the index.
     */
    public abstract MetadataFieldMapper timeSeriesIdFieldMapper();
    /**
     * How {@code time_series_dimension} fields are handled by indices in this mode.
     */
    public abstract DocumentDimensions buildDocumentDimensions(IndexSettings settings);