Add specilized impl for array agg group accumulator

[rluvaton]

No description provided.

[rluvaton]

If self was mutable we would not be able to have special implementation for sorted

[alamb]

One way to to that would be potentially to use an enum:

enum ArrayAggGroupAccumulator {
  Unsorted {
    data_type: DataType,
    adapter: GroupsAccumulatorAdapter,
  },
  Sorted {
    inputs: Vec<ArrayRef>,
    lengths: Vec<usize>,
    // (group_index, length)
    current_group: Option<(usize, usize)>,
    item_data_type: DataType,
  }     
}

So this code would look lke

impl GroupsAccumulator for ArrayAggGroupAccumulator {

    fn with_group_indices_order_mode(
        &mut self,
        group_indices_order_mode: &datafusion_expr_common::ordering::InputOrderMode,
    ) -> Result<()> {
        if matches!(group_indices_order_mode, InputOrderMode::Sorted) {
            *self = Self::Sorted {
                inputs: vec![],
                lengths: vec![],
                current_group: None,
                item_data_type: self.data_type,
            };
        }
       Ok(())
   }
...

}

[rluvaton]

Yes, but this it has a cost rather for matching but I'm ok in using mutable as well