Modify the orca optimizer's processing of unionall distribution strat…

[Light-City]

Change logs

The orca optimizer currently returns the ANY policy for the first child of a unionall-like node, which will result in Gather Motion for the downstream children and a 1:n Redistribution for the upstream.

for example:

    ->  Redistribute Motion 1:3  (slice2)
       ->  Append  (cost=0.00..863.91 rows=18001 width=12)
          ->  Finalize Vec Aggregate
            ->  Gather Motion 3:1  (slice3; segments: 3)
		...
       ->  Gather Motion 3:1  (slice4; segments: 3)
          ->  HashAggregate

after:

    ->  Append  (cost=0.00..863.91 rows=18001 width=12)
       ->  Result  (cost=0.00..431.06 rows=1 width=12)
          ->  Redistribute Motion 1:3  (slice2)
            ->  Finalize Aggregate
               ->  Gather Motion 3:1  (slice3; segments: 3)
               ...
       ->  HashAggregate

When there are many nodes, the first plan will cause performance bottlenecks and need to be modified. Fortunately, the gpdb community has also modified th is. Commit is 0cd056a0a3d3c30a1d6d4479e67802b6673118c7.

Why are the changes needed?

1.Affect performance 2.Plan is unreasonable

Does this PR introduce any user-facing change?

yes, tpcds 167 query.

How was this patch tested?

yes.

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