Derive Combined Hashed Spec For Outer Joins - Patch

[THANATOSLAVA]

Issue: Community reports regression that post-fc662ea plans had redundant redistribution motion in inner joins

Root cause: Blanket change of Nulls Colocation to false in computing a matching hashed distribution spec

Solution: In matching a hashed distribution spec in inner join operations, set Nulls Colocation to true; and in matching a hashed distribution spec in outer join operations, set Nulls Colocation to false. This reflects the Nulls Colocation property required for / delivered by the outer relation in hash join operations.

Implementation: [CPhysicalHashJoin] -- Return Nulls Colocation in spec matching for inner joins, and Non Nulls Colocation for outer joins. [CPhysicalLeftOuterHashJoin] -- Add TODO comment. Left outer join should be able to return a combined hash spec even when only one relation is hash distributed. [minidump] -- Space size change only. Added user's example to verify inner join matches the outer relation's Nulls Colocation.

(cherry picked from commit 35f77dc0a5bd64aedc72fad6b861562b9c167bcd)

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[vraghavan78]

This needs to go to master first. Correct?

[gpopt]

@vraghavan78 Yes. PR for master: https://github.com/greenplum-db/gpdb/pull/13957