### What changes were proposed in this pull request?
This pr intends to fix wrong aggregated values in `GROUPING SETS` when there are duplicated grouping sets in a query (e.g., `GROUPING SETS ((k1),(k1))`).
For example;
```
scala> spark.table("t").show()
+---+---+---+
| k1| k2| v|
+---+---+---+
| 0| 0| 3|
+---+---+---+
scala> sql("""select grouping_id(), k1, k2, sum(v) from t group by grouping sets ((k1),(k1,k2),(k2,k1),(k1,k2))""").show()
+-------------+---+----+------+
|grouping_id()| k1| k2|sum(v)|
+-------------+---+----+------+
| 0| 0| 0| 9| <---- wrong aggregate value and the correct answer is `3`
| 1| 0|null| 3|
+-------------+---+----+------+
// PostgreSQL case
postgres=# select k1, k2, sum(v) from t group by grouping sets ((k1),(k1,k2),(k2,k1),(k1,k2));
k1 | k2 | sum
----+------+-----
0 | 0 | 3
0 | 0 | 3
0 | 0 | 3
0 | NULL | 3
(4 rows)
// Hive case
hive> select GROUPING__ID, k1, k2, sum(v) from t group by k1, k2 grouping sets ((k1),(k1,k2),(k2,k1),(k1,k2));
1 0 NULL 3
0 0 0 3
```
[MS SQL Server has the same behaviour with PostgreSQL](https://github.com/apache/spark/pull/26961#issuecomment-573638442). This pr follows the behaviour of PostgreSQL/SQL server; it adds one more virtual attribute in `Expand` for avoiding wrongly grouping rows with the same grouping ID.
### Why are the changes needed?
To fix bugs.
### Does this PR introduce any user-facing change?
No.
### How was this patch tested?
The existing tests.
Closes#26961 from maropu/SPARK-29708.
Authored-by: Takeshi Yamamuro <yamamuro@apache.org>
Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>
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