### What changes were proposed in this pull request?
This pr add row count to `Union` operator when CBO enabled.
```scala
spark.sql("CREATE TABLE t1 USING parquet AS SELECT id FROM RANGE(10)")
spark.sql("CREATE TABLE t2 USING parquet AS SELECT id FROM RANGE(10)")
spark.sql("ANALYZE TABLE t1 COMPUTE STATISTICS FOR ALL COLUMNS")
spark.sql("ANALYZE TABLE t2 COMPUTE STATISTICS FOR ALL COLUMNS")
spark.sql("set spark.sql.cbo.enabled=true")
spark.sql("SELECT * FROM t1 UNION ALL SELECT * FROM t2").explain("cost")
```
Before this pr:
```
== Optimized Logical Plan ==
Union false, false, Statistics(sizeInBytes=320.0 B)
:- Relation[id#5880L] parquet, Statistics(sizeInBytes=160.0 B, rowCount=10)
+- Relation[id#5881L] parquet, Statistics(sizeInBytes=160.0 B, rowCount=10)
```
After this pr:
```
== Optimized Logical Plan ==
Union false, false, Statistics(sizeInBytes=320.0 B, rowCount=20)
:- Relation[id#2138L] parquet, Statistics(sizeInBytes=160.0 B, rowCount=10)
+- Relation[id#2139L] parquet, Statistics(sizeInBytes=160.0 B, rowCount=10)
```
### Why are the changes needed?
Improve query performance, [`JoinEstimation.estimateInnerOuterJoin`](d6a68e0b67/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/JoinEstimation.scala (L55-L156)) need the row count.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Unit test.
Closes#31068 from wangyum/SPARK-34031.
Lead-authored-by: Yuming Wang <yumwang@ebay.com>
Co-authored-by: Hyukjin Kwon <gurwls223@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
aa509c1eee