fix: Implicitly plan UNNEST as lateral

[rkrishn7]

Which issue does this PR close?

Partial fix for #13659

Rationale for this change

Fixes support for implicitly planning table functions in the FROM clause as lateral.

What changes are included in this PR?

This PR adds support for implicit lateral planning of UNNEST table factors.

Are these changes tested?

Yes, sqllogictest added.

Are there any user-facing changes?

Potentially - because UNNEST is now implicitly lateral, like Postgres. However, since outer references still fail in the query planning/optimization phase, I'm not sure if documentation updates are required.

[goldmedal]

I think it's better to add a logical plan test like

explain select * from unnest_table u, unnest(u.column1);

You can refer to how other LATERAL tests do it.

[rkrishn7]

Added!

[goldmedal]

It's good to keep this one and another planning one in the sqllogictest (for end-to-end SQL test).

Just like the following case:

datafusion/datafusion/sqllogictest/test_files/joins.slt

Lines 4051 to 4053 in d3cfc45

	# Test CROSS JOIN LATERAL syntax (planning)
	query TT
	explain select t1_id, t1_name, i from join_t1 t1 cross join lateral (select * from unnest(generate_series(1, t1_int))) as series(i);

and

datafusion/datafusion/sqllogictest/test_files/joins.slt

Lines 4068 to 4072 in d3cfc45

	# Test CROSS JOIN LATERAL syntax (execution)
	# TODO: https://github.com/apache/datafusion/issues/10048
	query error DataFusion error: This feature is not implemented: Physical plan does not support logical expression OuterReferenceColumn\(UInt32, Column \{ relation: Some\(Bare \{ table: "t1" \}\), name: "t1_int" \}\)
	select t1_id, t1_name, i from join_t1 t1 cross join lateral (select * from unnest(generate_series(1, t1_int))) as series(i);

[alamb]

Thank you @rkrishn7

Can you please add some slt tests that actually run this kind of query to show them working and generating correct results?

Thank you 🙏

[alamb]

BTW, here are the instructions for sqllogictests: https://github.com/apache/datafusion/tree/main/datafusion/sqllogictest

Ideally you should be able to extend one of the existing test files in https://github.com/apache/datafusion/tree/main/datafusion/sqllogictest/test_files

[rkrishn7]

@alamb @goldmedal

Added a few slt tests! Apologies for the delay!

[goldmedal]

Thanks @rkrishn7 it looks good to me.

[alamb]

Thanks @rkrishn7 and @goldmedal !