Preserve aggregate results for outer joins without criteria

[bvolpato]

Description

Preserve aggregate results when an outer join has no equijoin criteria. Pushing aggregation below such a join creates a global aggregation, which emits a row even when its input is empty. That changes count(*) over the preserved outer row from 1 to 0.

SELECT count(*)
FROM (VALUES 1) l(a)
LEFT JOIN (
    SELECT * FROM UNNEST(CAST(ARRAY[] AS array(integer)))
) r(b) ON true;

This returns 0 before the fix and 1 afterward. The rule now skips joins without equijoin criteria. Regressions cover LEFT and RIGHT joins and grouped counts.

Additional context and related issues

Existing equijoin aggregation pushdown remains covered by the rule tests. The five new regressions failed before the production change. Afterward, all 25 tests in TestJoin and TestPushAggregationThroughOuterJoin passed. Maven validate, including Checkstyle and Airstyle, passed for core/trino-main.

./mvnw -pl core/trino-main -Dtest=TestJoin,TestPushAggregationThroughOuterJoin -Dair.check.skip-all=true test
./mvnw -pl core/trino-main validate

Downsides

Aggregations over outer joins without equijoin criteria can process more intermediate rows because this pushdown is no longer applied.

Release notes

(x) Release notes are required, with the following suggested text:

## General
* Fix incorrect aggregate results for outer joins without equijoin criteria when the inner input is empty.

[findepi]

"empty left join" is kinda misleading. the join result is not empty. it's the right side of the left join who's empty.

let's call it testCountOverOuterJoinWithEmptyInnerSide and let's merge the RIGHT JOIN test case (testCountOverEmptyRightJoin) with this test mehod

[findepi]

Suggested change

	public void testCountOverEmptyLeftJoin()
	public void testCountOverOuterJoinWithEmptyInnerSide()

[findepi]

Suggested change

	}
	@Test
	public void testCountOverEmptyRightJoin()
	{

[findepi]

rename appropriately, see above