fix: failed to create ValuesExec with non-nullable schema

[jonahgao]

Which issue does this PR close?

Closes #8763.

Rationale for this change

In ValuesExec::try_new, we use the schema of ValuesExec and null arrays to construct a placeholder batch.
https://github.com/apache/arrow-datafusion/blob/dd4263f843e093c807d63edf73a571b1ba2669b5/datafusion/physical-plan/src/values.rs#L56-L64
This batch placeholder is used to evaluate the physical expressions in Values.

But users can define a schema containing non-nullable fields for ValuesExec just like issue #8763, which is in conflict with null arrays.

let field = Field::new("a", DataType::Int32, false);
let schema = Schema::new(vec![field]);
let df_schema = DFSchema::try_from(schema.clone()).unwrap();
let values = vec![vec![Expr::Literal(ScalarValue::Int32(Some(1)))]];
let values_plan = LogicalPlan::Values(Values {
        schema: df_schema.clone().into(),
        values: values.clone(),
})

In this case, an ArrowError ‘InvalidArgumentError("Column 'a' is declared as non-nullable but contains null values"))' will be raised.

Since ValuesExec has no input, I think the schema for this placeholder batch can be empty, rather than using the schema from ValuesExec.

What changes are included in this PR?

Use correct schema to build the placeholder batch in ValuesExec::try_new.

Are these changes tested?

Yes

Are there any user-facing changes?

No

[jonahgao]

Returning ScalarValue::List(a) makes the following query fail.

DataFusion CLI v34.0.0
❯ select * from (values(random()));
Internal error: Inconsistent types in ScalarValue::iter_to_array. Expected Float64, got List(0.5174512019067328).
This was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker

Related to pr #7629. I think it's a bug, so I fixed it.

[alamb]

Looks good to me -- thank you @jonahgao

[alamb]

👍

[alamb]

👍 this code to use a null array probably pre-dates the ability to create zero column record batches

[alamb]

Also thank you for:

1. The very clear PR description
2. The drive by cleanups to comments
3. The fix of the other bug you found (and the clear comments and tests) 🙏

Very much appreciated

[jonahgao]

Thank you for reviewing @alamb .