[SPARK-28272][SQL][PYTHON][TESTS] Convert and port 'pgSQL/aggregates_part3.sql' into UDF test base

[HyukjinKwon]

What changes were proposed in this pull request?

This PR proposes to port pgSQL/aggregates_part3.sql into UDF test base.

Diff comparing to 'pgSQL/aggregates_part3.sql'

diff --git a/sql/core/src/test/resources/sql-tests/results/pgSQL/aggregates_part3.sql.out b/sql/core/src/test/resources/sql-tests/results/udf/pgSQL/udf-aggregates_part3.sql.out
index f102383cb4d..eff33f280cf 100644
--- a/sql/core/src/test/resources/sql-tests/results/pgSQL/aggregates_part3.sql.out
+++ b/sql/core/src/test/resources/sql-tests/results/udf/pgSQL/udf-aggregates_part3.sql.out
@@ -3,7 +3,7 @@


 -- !query 0
-select max(min(unique1)) from tenk1
+select udf(max(min(unique1))) from tenk1
 -- !query 0 schema
 struct<>
 -- !query 0 output
@@ -12,11 +12,11 @@ It is not allowed to use an aggregate function in the argument of another aggreg


 -- !query 1
-select (select count(*)
-        from (values (1)) t0(inner_c))
+select udf((select udf(count(*))
+        from (values (1)) t0(inner_c))) as col
 from (values (2),(3)) t1(outer_c)
 -- !query 1 schema
-struct<scalarsubquery():bigint>
+struct<col:bigint>
 -- !query 1 output
 1
 1

Why are the changes needed?

To improve test coverage in UDFs.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Manually tested via:

 build/sbt "sql/test-only *SQLQueryTestSuite -- -z udf/pgSQL/udf-aggregates_part3.sql"

as guided in https://issues.apache.org/jira/browse/SPARK-27921

[SparkQA]

Test build #110158 has finished for PR 25676 at commit f9aab42.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

I am just going to merge this. This is pretty straightforward.