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.

首先阅读 SQL 示例中描述的过滤和投影行为，包括 ProjectionExec 以及 projection-pushdown issue #14993。确定如何表示和计算重复表达式（例如 variant_get(col, 'key')），然后将完成定义为：在保留查询结果的同时避免重复计算。

由索引模型根据 Issue 内容生成。