Move Item_func::count_xxx_length() to Type_std_attributes

void count_only_length(Item **item, uint nitems);

void count_octet_length(Item **item, uint nitems);

void count_real_length(Item **item, uint nitems);

void count_decimal_length(Item **item, uint nitems);

bool count_string_length(Item **item, uint nitems);

uint count_max_decimals(Item **item, uint nitems)

{

  uint res= 0;

  for (uint i= 0; i < nitems; i++)

    set_if_bigger(res, item[i]->decimals);

  return res;

}

void aggregate_attributes_int(Item **items, uint nitems);

void aggregate_attributes_real(Item **items, uint nitems);

void aggregate_attributes_decimal(Item **items, uint nitems);

bool aggregate_attributes_string(Item **item, uint nitems);

void aggregate_attributes_temporal(uint int_part_length,

                                   Item **item, uint nitems);