Updating segment map function for QueryDataSource to ensure group by …

[somu-imply]

…of group by of join data source gets into proper segment map function path

A query such as

{
    "queryType": "groupBy",
    "dimensions": ["related_object_id", "r.category_id"],
    "dataSource":
    {
        "type": "query",
        "query":
        {
            "queryType": "groupBy",
            "dimensions": ["related_object_id","r.category_id"],
            "intervals": "2020-03-20/2020-03-21",
            "dataSource":
            {
                "type": "join",
                "left":
                {
                    "type": "inline",
                    "name": "DRUID_INLINE_DATASOURCE",
                    "columnNames":
                    [
                        "__time",
                        "related_object_id"
                    ],
                    "rows":
                    [
                        [1584662400000,"3229"],
                        [1584662400000,"4510"]
                    ]
                },
                "right":
                {
                    "type": "inline",
                    "columnNames":
                    ["related_object_id","category_id"],
                    "rows":
                    [
                        ["3229", 2985],
                        ["4510", 2985]
                    ]
                },
                "rightPrefix": "r.",
                "condition": "related_object_id == \"r.related_object_id\"",
                "joinType": "LEFT"
            },
            "granularity": "day",
            "filter":
            {
                "type": "in",
                "dimension": "related_object_id",
                "values":
                [
                    "3229",
                    "4510"
                ]
            }
        }
    },
    "intervals": "2020-03-20/2020-03-21",
    "granularity": "all",
}

was producing nulls as the Segment map function of Join was not called as the Inner Query Data source's segment map function was returning an identity function. Changed the query data source's segment map function which should delegate to the segment map function of the subquery's datasource. The test now passes.

Fixes #14088

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[somu-imply]

Although I added the test, the change in processing might not be covered and there might be a lack of coverage. But the issue is fixed with this. The screenshot is attached.

[imply-cheddar]

If you additionally add a test to the QueryDataSourceTest that calls the segment MapFn method and validates that it returns the thing that its child returned (you should be able to do this relatively easily by passing in a child Query object that you can control), then you can get coverage for the lines as well.

[imply-cheddar]

Approving as this is good for now. But please add the test to QueryDataSourceTest so that coverage robot is happy too.