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

ColumnNumbers getArgumentsThatAreAlwaysConstant() const override { return {1, 2}; }
    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr &, size_t ) const override
    {
        const auto & col_type_name = arguments[0];
        const ColumnPtr & column = col_type_name.column;
        const auto & col_ipv6_zeroed_tail_bytes_type = arguments[1];
        const auto & col_ipv6_zeroed_tail_bytes = col_ipv6_zeroed_tail_bytes_type.column;
        const auto & col_ipv4_zeroed_tail_bytes_type = arguments[2];
        const auto & col_ipv4_zeroed_tail_bytes = col_ipv4_zeroed_tail_bytes_type.column;
        if (const auto * col_in = checkAndGetColumn<ColumnFixedString>(column.get()))
        {
            if (col_in->getN() != IPV6_BINARY_LENGTH)
                throw Exception("Illegal type " + col_type_name.type->getName() +
                                " of column " + col_in->getName() +
                                " argument of function " + getName() +
                                ", expected FixedString(" + toString(IPV6_BINARY_LENGTH) + ")",
                                ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);