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

#include <Functions/FunctionFactory.h>
#include <Functions/FunctionsCoding.h>
namespace DB
{
struct NameFunctionIPv4NumToString { static constexpr auto name = "IPv4NumToString"; };
struct NameFunctionIPv4NumToStringClassC { static constexpr auto name = "IPv4NumToStringClassC"; };
void registerFunctionsCoding(FunctionFactory & factory)
{
    factory.registerFunction<FunctionToStringCutToZero>();
    factory.registerFunction<FunctionCutIPv6>();
    factory.registerFunction<FunctionIPv4ToIPv6>();
    factory.registerFunction<FunctionMACNumToString>();