PostgreSQL compatibility: `regexp_replace` should honor PostgreSQL multiline flag `m`

Split out from #22247.

### Mismatch

`regexp_replace` should honor PostgreSQL multiline flag `m`.

```sql
SELECT regexp_replace(E'a\nb', '^b', 'x', 'm');
```

PostgreSQL:

```text
a
x
```

DataFusion:

```text
a\nb
```

### Expected behavior

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