**Describe the situation**
multiIf works 10 times slower than If with single condition.

**How to reproduce**
ClickHouse version 21.10

```

SELECT count()
FROM numbers_mt(1000000000)
WHERE NOT ignore(multiIf(number = 0, NULL, toNullable(number)))

┌────count()─┐
│ 1000000000 │
└────────────┘

1 rows in set. Elapsed: 10.267 sec. Processed 1.00 billion rows, 8.00 GB (97.41 million rows/s., 779.25 MB/s.)

SELECT count()
FROM numbers_mt(1000000000)
WHERE NOT ignore(If(number = 0, NULL, toNullable(number)))

┌────count()─┐
│ 1000000000 │
└────────────┘

1 rows in set. Elapsed: 1.010 sec. Processed 1.00 billion rows, 8.00 GB (990.63 million rows/s., 7.93 GB/s.)
```

**Expected performance**
The same performance for multiIf and if.

if (settings.enable_positional_arguments)
            {
                const auto & value = group_exprs[i]->as<ASTLiteral>()->value;
                if (value.getType() == Field::Types::UInt64)
                {
                    auto pos = value.get<UInt64>();
                    if (pos > 0 && pos <= select_query->select()->children.size())
                        keep_position = true;
                }
            }
            if (keep_position)
                ++i;
            else
                remove_expr_at_index(i);
        }
        else
        {
            
            ++i;
        }
    }
    if (group_exprs.empty())
        appendUnusedGroupByColumn(select_query);
}
struct GroupByKeysInfo
{
    NameSet key_names; 
    bool has_function = false;
};
GroupByKeysInfo getGroupByKeysInfo(const ASTs & group_by_keys)