Looks like bfloat16 quantiles don't provide a way to specify the weight:

```sql
SELECT quantileBFloat16Weighted(0.5)(number, number)
FROM numbers(100)

Received exception from server (version 21.8.3):
Code: 46. DB::Exception: Received from localhost:9000. DB::Exception: Unknown function quantileBFloat16Weighted
```

But I expect it to work the same way as tdigest:

```sql
SELECT quantileTDigestWeighted(0.5)(number, number)
FROM numbers(100)

Query id: ea66ede3-afc6-4e5d-8949-2da5970e1349

┌─quantileTDigestWeighted(0.5)(number, number)─┐
│                                     70.35461 │
└──────────────────────────────────────────────┘
```

/cc @RedClusive just in case :)
AggregateFunctionQuantile<Value, Data, Name, has_second_arg, FloatReturnType, returns_many>>
{
private:
    using ColVecType = std::conditional_t<IsDecimalNumber<Value>, ColumnDecimal<Value>, ColumnVector<Value>>;
    static constexpr bool returns_float = !(std::is_same_v<FloatReturnType, void>);
    static_assert(!IsDecimalNumber<Value> || !returns_float);
    QuantileLevels<Float64> levels;
    
    Float64 level = 0.5;
    DataTypePtr & argument_type;
public:
    AggregateFunctionQuantile(const DataTypes & argument_types_, const Array & params)