Method order_by_with_nulls

src/query/helper.rs:667–674

Add an order_by expression with nulls ordering option ``` use sea_orm::{entity::*, query::*, tests_cfg::cake, DbBackend}; use sea_query::NullOrdering; assert_eq!( cake::Entity::find() .order_by_with_nulls(cake::Column::Id, Order::Asc, NullOrdering::First) .build(DbBackend::Postgres) .to_string(), r#"SELECT "cake"."id", "cake"."name" FROM "cake" ORDER BY "cake"."id" ASC NULLS FIRST"# ); ```

(mut self, col: C, ord: Order, nulls: NullOrdering)

    /// );
    /// ```
    fn order_by_with_nulls<C>(mut self, col: C, ord: Order, nulls: NullOrdering) -> Self
    where
        C: IntoSimpleExpr,
    {
        self.query()
            .order_by_expr_with_nulls(col.into_simple_expr(), ord, nulls);
        self
    }
}

// LINT: when the column does not appear in tables selected from