Currently arrayCompact doesn't work with tuples like other array functions arraySort or arrayFilter.
Please consider adding such functionality to arrayCompact.
We need something like this... SELECT arrayCompact( (x,y) -> y, arr1, arr2) AS v

Current behavior:
`SELECT
    [('a', 1), ('a', 2), ('c', 3), ('a', 2)] AS arr,
    arrayCompact(x -> (x.1), arr) AS v,
    [('a', 1), ('c', 3), ('a', 2)] AS expected_v
`
![изображение](https://user-images.githubusercontent.com/33029350/93028896-5fca5e00-f617-11ea-9d55-e0a5d3c36697.png)


size_t src_offsets_size = src_offsets.size();
        auto res_offsets_column = ColumnArray::ColumnOffsets::create(src_offsets_size);
        IColumn::Offsets & res_offsets = res_offsets_column->getData();
        size_t res_pos = 0;
        size_t src_pos = 0;
        for (size_t i = 0; i < src_offsets_size; ++i)
        {
            auto src_offset = src_offsets[i];
            
            if (src_pos < src_offset)
            {
                
                res_values_column->insertFrom(*mapped, src_pos);
                
                ++src_pos;
                ++res_pos;
                for (; src_pos < src_offset; ++src_pos)
                {
                    if (mapped->compareAt(src_pos - 1, src_pos, *mapped, 1))
                    {
                        res_values_column->insertFrom(*mapped, src_pos);
                        ++res_pos;
                    }
                }
            }
            res_offsets[i] = res_pos;
        }
        res_ptr = ColumnArray::create(std::move(res_values_column), std::move(res_offsets_column));
    }
    static ColumnPtr execute(const ColumnArray & array, ColumnPtr mapped)