ES|QL: Folding of REPLACE with constants throws ClassCastException

```
row txt = "a" |  WHERE MATCH(txt, REPLACE("XS", "X", "U"))
```


```
class java.lang.String cannot be cast to class org.apache.lucene.util.BytesRef (java.lang.String is in module java.base of loader 'bootstrap'; org.apache.lucene.util.BytesRef is in module org.apache.lucene.core@10.2.1 of loader 'app')
```