Avoid re-evaluating expressions in filters and projections

This patterns shows up pretty often:

```sql
select expensive(col)
from t
where expensive(col)
```

A pathological case is variant / json:

```sql
select variant_get(col, 'key')
from t
from variant_get(col, 'key')
```

There's two issues here:
1. Until we solve projection pushdown (https://github.com/apache/datafusion/issues/14993) if `key` is not shredded we materialize the entire `col` and then extract `key` in a `ProjectionExec`.
2. Even once that is resolved, or in the case that `key` is not shredded evaluating `variant_get(col, 'key')` itself is expensive we still re-compute `variant_get(col, 'key')` twice: once for the filter and once for the projection.

Inizia leggendo il comportamento di filtro e proiezione descritto negli esempi SQL, inclusi ProjectionExec e il problema di projection-pushdown #14993. Determina come vengono rappresentate e valutate le espressioni ripetute, come variant_get(col, 'key'), quindi definisci il completamento come l'evitare valutazioni duplicate preservando i risultati della query.

Scritto dal modello di indicizzazione a partire dal testo della issue.