**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 (!select_query->groupBy())
        return;
    auto group_by = select_query->groupBy();
    const auto & group_by_keys = group_by->children;
    ASTs modified; 
    GroupByKeysInfo group_by_keys_data = getGroupByKeysInfo(group_by_keys);
    if (!group_by_keys_data.has_function)
        return;
    GroupByFunctionKeysVisitor::Data visitor_data{group_by_keys_data.key_names};
    GroupByFunctionKeysVisitor(visitor_data).visit(group_by);
    modified.reserve(group_by_keys.size());
    
    for (const auto & group_key : group_by_keys)
        if (group_by_keys_data.key_names.contains(group_key->getColumnName()))
            modified.push_back(group_key);
    
    group_by->children = modified;
}
void optimizeAggregateFunctionsOfGroupByKeys(ASTSelectQuery * select_query, ASTPtr & node)