Allow to unparse UNNEST plan back to a table function SQL text

[goldmedal]

Is your feature request related to a problem or challenge?

Given a SQL:

select * from unnest([1,2,3]) as t(c1)

DataFusion plans the unnest to Projection/Unnest/Projection pattern like

Projection: *
  SubqueryAlias: t
    Projection: UNNEST(make_array(Int64(1),Int64(2),Int64(3))) AS c1
      Projection: unnest_placeholder(make_array(Int64(1),Int64(2),Int64(3)),depth=1) AS UNNEST(make_array(Int64(1),Int64(2),Int64(3)))
        Unnest: lists[unnest_placeholder(make_array(Int64(1),Int64(2),Int64(3)))|depth=1] structs[]
          Projection: make_array(Int64(1), Int64(2), Int64(3)) AS unnest_placeholder(make_array(Int64(1),Int64(2),Int64(3)))
            EmptyRelation

If we try to unparse the plan back to the SQL, the result is

SELECT * FROM (SELECT UNNEST([1, 2, 3]) AS "UNNEST(make_array(Int64(1),Int64(2),Int64(3)))") AS t (c1)

However, some databases (e.g. BigQuery), only support using UNNEST as a table function.

Describe the solution you'd like

We can introduce a new option for the unparser Dialect

pub trait Dialect: Send + Sync {
    ...
    /// Allow to unparse the unnest plan as a table function.
    fn unnest_as_table_function(&self) -> bool {
        false
    }
    ...
}

If we found the pattern of plan like Projection/Unnest/Projection, we can try to unparse it to an ast::query::TableFactor::UNNEST.

Describe alternatives you've considered

No response

Additional context

We may need to ignore other instances of UNNEST usage, such as:

SELECT UNNEST(column1), UNNEST(column2) FROM (SELECT column1, column2 FROM xxx);

This issue aims to enable a roundtrip for the UNNEST table function.

[jatin510]

take