**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]      │
└─────────┴──────────────┘
```

ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t ) const override
    {
        const ColumnPtr & column = arguments[0].column;
        if (const ColumnString * col = checkAndGetColumn<ColumnString>(column.get()))
        {
            auto col_res = ColumnUInt64::create();
            ColumnUInt64::Container & vec_res = col_res->getData();
            vec_res.resize(col->size());
            const ColumnString::Chars & vec_src = col->getChars();
            const ColumnString::Offsets & offsets_src = col->getOffsets();
            size_t prev_offset = 0;
            for (size_t i = 0; i < vec_res.size(); ++i)
            {
                size_t current_offset = offsets_src[i];
                size_t string_size = current_offset - prev_offset - 1; 
                if (string_size >= Impl::min_string_size && string_size <= Impl::max_string_size)
                    vec_res[i] = Impl::parse(reinterpret_cast<const char *>(&vec_src[prev_offset]));
                else
                    vec_res[i] = 0;
                prev_offset = current_offset;
            }
            return col_res;
        }
        else
            throw Exception("Illegal column " + arguments[0].column->getName()
                + " of argument of function " + getName(),
                ErrorCodes::ILLEGAL_COLUMN);
    }
};
class FunctionUUIDNumToString : public IFunction