### What changes were proposed in this pull request?
While adding new partition to v2 `InMemoryAtomicPartitionTable`/`InMemoryPartitionTable`, add single row to the table content when the table is fully partitioned.
### Why are the changes needed?
The `ALTER TABLE .. ADD PARTITION` command does not change content of fully partitioned v2 table. For instance, `INSERT INTO` changes table content:
```scala
sql(s"CREATE TABLE t (p0 INT, p1 STRING) USING _ PARTITIONED BY (p0, p1)")
sql(s"INSERT INTO t SELECT 1, 'def'")
sql(s"SELECT * FROM t").show(false)
+---+---+
|p0 |p1 |
+---+---+
|1 |def|
+---+---+
```
but `ALTER TABLE .. ADD PARTITION` doesn't change v2 table content:
```scala
sql(s"ALTER TABLE t ADD PARTITION (p0 = 0, p1 = 'abc')")
sql(s"SELECT * FROM t").show(false)
+---+---+
|p0 |p1 |
+---+---+
+---+---+
```
### Does this PR introduce _any_ user-facing change?
No, the changes impact only on tests but for the example above in tests:
```scala
sql(s"ALTER TABLE t ADD PARTITION (p0 = 0, p1 = 'abc')")
sql(s"SELECT * FROM t").show(false)
+---+---+
|p0 |p1 |
+---+---+
|0 |abc|
+---+---+
```
### How was this patch tested?
By running the unified tests for `ALTER TABLE .. ADD PARTITION`.
Closes#31216 from MaxGekk/add-partition-by-all-columns.
Authored-by: Max Gekk <max.gekk@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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