Unparser broken with `IS DISTINCT FROM` statements

[cetra3]

Describe the bug

The Unparser doesn't support IS DISTINCT FROM in statements. This break things, especially with the new array_has null semantics (#21743) and optimizer passes.

I.e, the following fails outright in the unparser:

SELECT value IS DISTINCT FROM 1 FROM t

The following fails after an optimization pass:

SELECT CASE WHEN value > 0 THEN true ELSE false END FROM t

To Reproduce

Simple to fail:

#[tokio::test]
async fn unparse_is_distinct_from() -> Result<()> {
    let ctx = SessionContext::new();

    let schema = Arc::new(Schema::new(vec![Field::new(
        "value",
        DataType::Int32,
        true,
    )]));
    ctx.register_table("t", Arc::new(MemTable::try_new(schema, vec![vec![]])?))?;

    let df = ctx
        .sql("SELECT value IS DISTINCT FROM 1 FROM t")
        .await?;

    let sql = plan_to_sql(df.logical_plan())?;

    Ok(())
}

Expected behavior

No response

Additional context

No response