**Use case**

Convert bitmask to position.
It would allow us to directly use FLAT dictionary or Enum datatype without jumping around slow `bitmasktoArray` and `arrayMap`

**Describe the solution you'd like**

```
SELECT
    arrayMap(x -> log2(x), bitmaskToArray(100)) AS bitmask,
    bitPositions(100)  AS bitpositions

┌─bitmask─┬─bitpositions─┐
│ [2,5,6] │ [2,5,6]      │
└─────────┴──────────────┘
```

{
        if (!isInteger(arguments[0]))
            throw Exception("Illegal type " + arguments[0]->getName() + " of argument of function " + getName(),
            ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        return std::make_shared<DataTypeArray>(arguments[0]);
    }
    bool useDefaultImplementationForConstants() const override { return true; }
    template <typename T>
    bool tryExecute(const IColumn * column, ColumnPtr & out_column) const
    {
        using UnsignedT = make_unsigned_t<T>;
        if (const ColumnVector<T> * col_from = checkAndGetColumn<ColumnVector<T>>(column))
        {
            auto col_values = ColumnVector<T>::create();
            auto col_offsets = ColumnArray::ColumnOffsets::create();
            typename ColumnVector<T>::Container & res_values = col_values->getData();
            ColumnArray::Offsets & res_offsets = col_offsets->getData();
            const typename ColumnVector<T>::Container & vec_from = col_from->getData();
            size_t size = vec_from.size();
            res_offsets.resize(size);
            res_values.reserve(size * 2);
            for (size_t row = 0; row < size; ++row)
            {
                UnsignedT x = vec_from[row];
                while (x)
                {
                    UnsignedT y = x & (x - 1);
                    UnsignedT bit = x ^ y;
                    x = y;
                    res_values.push_back(bit);