Cosmos: Stop nesting results in an extra JSON object

[roji]

Our basic Cosmos query looks like this:

SELECT c FROM root c

This produces results such as the following:

[
    {
        "c": {
            "id": "...",
            "Foo": 1,
        }
    },
    {
        "c": {
            "id": "...",
            "Foo": 2,
        }
    }
]

Instead, we could generate the following simpler star-based query:

SELECT VALUE c FROM root c

Which produces:

[
    {
        "id": "...",
        "Foo": 1,
    },
    {
        "id": "...",
        "Foo": 2,
    }
]

[ajcvickers]

Note: breaking change because it impacts raw queries.

[roji]

This creates issues since subqueries need to project out the bare object, rather than an object wrapping the object (interferes with query). We could have different logic for top-level projections (which are processed by the shaper) and subquery projections (which aren't), but we really should just do the right thing.

[roji]

Example test for trivial scalar projection, NorthwindSelectQueryTestBase.Select_scalar:

public virtual Task Select_scalar(bool async)
    => AssertQuery(
        async,
        ss => ss.Set<Customer>().Select(c => c.City));

Currently-generated NoSQL:

SELECT c["City"]
FROM root c
WHERE (c["Discriminator"] = "Customer")

Cosmos results:

[
    {
        "City": "Berlin"
    },
    {
        "City": "México D.F."
    },
    {
        "City": "México D.F."
    },
    {
        "City": "London"
    },
    ...
]

Proposed NoSQL:

SELECT VALUE c["City"]
FROM root c
WHERE (c["Discriminator"] = "Customer")

Cosmos results:

[
    "Berlin",
    "México D.F.",
    "México D.F.",
    "London",
    ...
]

[roji]

And the same thing for a structural type projected out of the database, NorthwindSelectQueryTestBase.Select_customer_identity:

public virtual Task Select_customer_identity(bool async)
    => AssertQuery(
        async,
        ss => ss.Set<Customer>().Select(c => c));

Currently-generated NoSQL:

SELECT c
FROM root c
WHERE (c["Discriminator"] = "Customer")

Cosmos results:

[
    {
        "c": {
            "id": "Customer|ALFKI",
            ...
        }
    },
    {
        "c": {
            "id": "Customer|ANATR",
            ...
    },
    ....
]

Proposed NoSQL:

SELECT VALUE c
FROM root c
WHERE (c["Discriminator"] = "Customer")

Cosmos results:

[
    {
        "id": "Customer|ALFKI",
        ...
    },
    {
        "id": "Customer|ANATR",
        ...
    },
    ...
]