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

{
private:
    static inline std::pair<UInt32, UInt32> applyCIDRMask(UInt32 src, UInt8 bits_to_keep)
    {
        if (bits_to_keep >= 8 * sizeof(UInt32))
            return { src, src };
        if (bits_to_keep == 0)
            return { UInt32(0), UInt32(-1) };
        UInt32 mask = UInt32(-1) << (8 * sizeof(UInt32) - bits_to_keep);
        UInt32 lower = src & mask;
        UInt32 upper = lower | ~mask;
        return { lower, upper };
    }
public:
    static constexpr auto name = "IPv4CIDRToRange";
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionIPv4CIDRToRange>(); }