Scalar subquery can fail to reference unqualified field from outer query

[andygrove]

Describe the bug

The following query fails with SchemaError(FieldNotFound { qualifier: None, name: "j2_id", valid_fields: Some(["j1.j1_id", "j1.j1_string", "j3.j3_id", "j3.j3_string", "j1.j1_id", "j1.j1_string", "j3.j3_id", "j3.j3_string"]) }

SELECT j1_string, j2_string 
        FROM j1, j2 
        WHERE j1_id = j2_id - 1 
        AND j2_id < (SELECT count(*) 
            FROM j1, j3 
            WHERE j2_id = j1_id 
            AND j1_id = j3_id)

To Reproduce

Add this test to sql/planner.rs:

#[test]
fn scalar_subquery_reference_outer_field() {
    let sql = "SELECT j1_string, j2_string \
    FROM j1, j2 \
    WHERE j1_id = j2_id - 1 \
    AND j2_id < (SELECT count(*) \
        FROM j1, j3 \
        WHERE j2_id = j1_id \
        AND j1_id = j3_id)";

    let expected = "TBD";

    quick_test(sql, &expected);
}

Also, add these tables to MockContextProvider in the same file.

"j1" => Some(Schema::new(vec![
    Field::new("j1_id", DataType::Int32, false),
    Field::new("j1_string", DataType::Utf8, false),
])),
"j2" => Some(Schema::new(vec![
    Field::new("j2_id", DataType::Int32, false),
    Field::new("j2_string", DataType::Utf8, false),
])),
"j3" => Some(Schema::new(vec![
    Field::new("j3_id", DataType::Int32, false),
    Field::new("j3_string", DataType::Utf8, false),
])),

Expected behavior
Query should produce a valid plan.

Additional context
None