Fixed document source and score field mismatch in sorted hybrid queries

[martin-gaievski]

Fixed document source and score field mismatch in sorted hybrid queries.
Returned search hits identified with the help of min heap, it's used by sorting functionality to get top X docs. We do keep track of the heap leaf element and updating it when collecting doc ids. In current code we use only one element for this, but in case of hybrid query we do need separate element for each sub-query. With a single element our updates are incorrectly propagated to a results of different sub-queries, cause different types of inconsistency: doc id, score fields, score can be incorrect in final search result.

In this PR I'm changing the min heap leaf element from a single object to an array of objects, one for each sub-query.

Tested on the data set referred in the issue, got correct response where all field have consistent values in _source and sort sections:

{
    "took": 455,
    "timed_out": false,
    "_shards": {
        "total": 5,
        "successful": 5,
        "skipped": 0,
        "failed": 0
    },
    "hits": {
        "total": {
            "value": 397,
            "relation": "eq"
        },
        "max_score": 0.8442519,
        "hits": [
            {
                "_index": "templates_prod",
                "_id": "bk2m5np8h467r92kmalxdcvft",
                "_score": null,
                "_source": {
                    "trendingScore": 303.125,
                    "name": "Summer Breeze Design"
                },
                "sort": [
                    303.125
                ]
            },
            {
                "_index": "templates_prod",
                "_id": "bk2m6w28201xn8m3vb6mmdebn",
                "_score": null,
                "_source": {
                    "trendingScore": 303.125,
                    "name": "Winterfrost"
                },
                "sort": [
                    303.125
                ]
            },
            {
                "_index": "templates_prod",
                "_id": "ak2nhbsz900lwxe0xcpir0duc",
                "_score": null,
                "_source": {
                    "trendingScore": 19,
                    "name": "Sunshine Days - Nature Greeting"
                },
                "sort": [
                    19.0
                ]
            },
            {
                "_index": "templates_prod",
                "_id": "ak2n8y4h900csue0x7ij8rwuj",
                "_score": null,
                "_source": {
                    "trendingScore": 13,
                    "name": "Mountain Vista Wedding Suite - Save the Date"
                },
                "sort": [
                    13.0
                ]
            },
            {
                "_index": "templates_prod",
                "_id": "ak2nau2a900e7ue0x2h3nheb9",
                "_score": null,
                "_source": {
                    "trendingScore": 10,
                    "name": "Ocean Waves Thank You"
                },
                "sort": [
                    10.0
                ]
            },
            {
                "_index": "templates_prod",
                "_id": "ak305ic900fr3xe0xjuiin2nt",
                "_score": null,
                "_source": {
                    "trendingScore": 10,
                    "name": "Midnight Dreams - Elegant Celebration"
                },
                "sort": [
                    10.0
                ]
            },
            {
                "_index": "templates_prod",
                "_id": "ak2n2r1t007au00xsn82pvg1",
                "_score": null,
                "_source": {
                    "trendingScore": 6,
                    "name": "Forest Pine - Rustic Wedding Invitation"
                },
                "sort": [
                    6.0
                ]
            },
            {
                "_index": "templates_prod",
                "_id": "ak2n0pxe0060u00xxz0afuaa",
                "_score": null,
                "_source": {
                    "trendingScore": 3.0,
                    "name": "Modern Romance - Classic Black Wedding Invitation"
                },
                "sort": [
                    3.0
                ]
            }
        ]
    }
}

Related Issues

#1044

Check List

• New functionality includes testing.
• [ ] New functionality has been documented.
• [ ] API changes companion pull request created.
• Commits are signed per the DCO using --signoff.~~
• [ ] Public documentation issue/PR created.

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[vibrantvarun]

Suggested change

	private FieldValueHitQueue.Entry fieldValueLeafTrackers[];
	private FieldValueHitQueue.Entry sortFieldValueTrackers[];

[vibrantvarun]

QQ: Do you want this code to be executed
a. Once per shard?
b. Once per segment?
c. Once per entire search flow?

[vibrantvarun]

I think this code can be shifted under above if(compoundScores==null) condition.