[SPARK-3938][SQL] Names in-memory columnar RDD with corresponding table name

This PR enables the Web UI storage tab to show the in-memory table name instead of the mysterious query plan string as the name of the in-memory columnar RDD.

Note that after #2501, a single columnar RDD can be shared with multiple in-memory tables, as long as their query results are the same. In this case, only the first cached table name is shown. For example:

```sql
CACHE TABLE first AS SELECT * FROM src;
CACHE TABLE second AS SELECT * FROM src;
```

The Web UI only shows "In-memory table first".