SearchSource: fix docvalue_fields and fields intersection logic

[nreese]

There is a bug in SearchSource with the existing docvalue_fields and fields intersection logic.

https://github.com/elastic/kibana/blob/7.4/src/legacy/ui/public/courier/search_source/search_source.js#L573

flatData.body.docvalue_fields = _.intersection(flatData.body.docvalue_fields, fields);

The logic assumes that both flatData.body.docvalue_fields and fields is an array of strings. That is not the case. flatData.body.docvalue_fields is an array of objects as specified here.

This PR updates the intersection logic to account for the fact that docvalue_fields is an array of objects.

The PR also updates how the default docvalue_fields is assigned. The old logic unioned the provided docvalue_fields and those from getComputedFields. This made it impossible to remove getComputedFields.docvalue_fields that are also include in fields. If a search source provides docvalue_fields then it does not make sense to union with getComputedFields.docvalue_fields.

Below is the use case for the maps application that spurred these changes. The maps application would like to receive the date as epoch_millis so it can be treated like a number to style markers based on age. The maps application would also like to receive the geo_point geometry from doc_values so we do not have to parse the value from _source since there are 5 different accepted formats.

const initialSearchSourceState = {
  docvalue_fields: [
    {
      field: "@timestamp",
      format: "epoch_millis"
    },
    {
      field: "geo.coordinates",
    }
  ],
};
const searchSource = new SearchSource(initialSearchSourceState);

With the updates our request and response are what are expected

// ES _search request body
{
  "docvalue_fields": [
    {
      "field": "@timestamp",
      "format": "epoch_millis"
    },
    {
      "field": "geo.coordinates"
    }
  ],
  "size": 10000,
}

// ES _search response hit example
"hits": [
  {
    "_index": "kibana_sample_data_logs",
    "_type": "_doc",
    "_id": "R4P3bW0BXBg7ubMI10Mb",
    "_score": 0,
    "_source": {},
    "fields": {
      "geo.coordinates": [
        "47.547698873095214, -116.18850083090365"
      ],
      "@timestamp": [
        "1569522434527"
      ]
    }
  }
]

When the provided docvalue_fields are unioned with getComputedFields the following is returned. Notice the wasted bandwidth because @timestamp is now returned to 2 formats

// ES _search request body
{
  "docvalue_fields": [
    {
      "field": "@timestamp",
      "format": "epoch_millis"
    },
    {
      "field": "geo.coordinates"
    },
    {
      "field": "@timestamp",
      "format": "date_time"
    }
  ],
  "size": 10000,
}

// ES _search response hit example
"hits": [
  {
    "_index": "kibana_sample_data_logs",
    "_type": "_doc",
    "_id": "R4P3bW0BXBg7ubMI10Mb",
    "_score": 0,
    "_source": {},
    "fields": {
      "geo.coordinates": [
        "47.547698873095214, -116.18850083090365"
      ],
      "@timestamp": [
        "1569522434527",
        "2019-09-26T18:27:14.527Z"
      ]
    }
  }
]

cc @nickpeihl

[elasticmachine]

Pinging @elastic/kibana-app

[elasticmachine]

Pinging @elastic/kibana-gis

[elasticmachine]

💔 Build Failed

• continuous-integration/kibana-ci/pull-request

[elasticcla]

Hi @nreese, we have found your signature in our records, but it seems like you have signed with a different e-mail than the one used in your Git commit. Can you please add both of these e-mails into your Github profile (they can be hidden), so we can match your e-mails to your Github profile?

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[nreese]

@Bargs @lukasolson This is ready for review

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: ebe087c

[Bargs]

LGTM