PostgreSQL compatibility: `array_length` of an empty array dimension should be NULL

Split out from #22247.

### Mismatch

`array_length` of an empty array dimension should be NULL.

```sql
SELECT array_length(array[]::int[], 1);
```

PostgreSQL:

```text
NULL
```

DataFusion:

```text
0
```

### Expected behavior

For PostgreSQL-compatible SQL semantics, DataFusion should either match PostgreSQL's result or raise the same class of domain/semantic error.