Fix explain(locus) show NULL.

[avamingli]

I found several plan show locus NULL when explain(locus).
And a assertion added after plan created show more like that.
There are caused by different reasons, this pr fix all.

Reproduce:

 Locus: NULL

explain (locus, costs off)
select * from
  (select count(id) from t1 where id > 10) ss
  right join (values (1),(2),(3)) v(x) on true;
                             QUERY PLAN                              
---------------------------------------------------------------------
 Nested Loop Left Join
   Locus: Entry
   ->  Values Scan on "*VALUES*"
         Locus: General
   ->  Materialize
         Locus: NULL
         ->  Finalize Aggregate
               Locus: SingleQE
               ->  Gather Motion 3:1  (slice1; segments: 3)
                     Locus: SingleQE
                     ->  Partial Aggregate
                           Locus: Hashed
                           ->  Index Only Scan using t1_id_idx on t1
                                 Locus: Hashed
                                 Index Cond: (id > 10)
 Optimizer: Postgres query optimizer
(16 rows)

explain(locus, costs off) select * from mrs_t1 where exists (select x from mrs_t1 where x < -1);
                    QUERY PLAN                    
--------------------------------------------------
 Gather Motion 3:1  (slice1; segments: 3)
   Locus: Entry
   InitPlan 1 (returns $0)  (slice2)
     ->  Gather Motion 3:1  (slice3; segments: 3)
           Locus: Entry
           ->  Seq Scan on mrs_t1 mrs_t1_1
                 Locus: Hashed
                 Filter: (x < '-1'::integer)
   ->  Result
         Locus: Hashed
         One-Time Filter: $0
         ->  Seq Scan on mrs_t1
               Locus: NULL
 Optimizer: Postgres query optimizer
(14 rows)

explain(locus, costs off) select * from mrs_t1 where exists (select x from mrs_t1 where x = 1);
                    QUERY PLAN                    
--------------------------------------------------
 Gather Motion 3:1  (slice1; segments: 3)
   Locus: Entry
   InitPlan 1 (returns $0)  (slice2)
     ->  Gather Motion 1:1  (slice3; segments: 1)
           Locus: Entry
           ->  Seq Scan on mrs_t1 mrs_t1_1
                 Locus: Hashed
                 Filter: (x = 1)
   ->  Result
         Locus: Hashed
         One-Time Filter: $0
         ->  Seq Scan on mrs_t1
               Locus: NULL
 Optimizer: Postgres query optimizer
(14 rows)

explain(locus, costs off) select * from mrs_t1 where x in (select x-95 from mrs_t1) or x < 5;
                        QUERY PLAN                         
-----------------------------------------------------------
 Gather Motion 3:1  (slice1; segments: 3)
   Locus: Entry
   ->  Seq Scan on mrs_t1
         Locus: Hashed
         Filter: ((hashed SubPlan 1) OR (x < 5))
         SubPlan 1
           ->  Broadcast Motion 3:3  (slice2; segments: 3)
                 Locus: NULL
                 ->  Seq Scan on mrs_t1 mrs_t1_1
                       Locus: Hashed
 Optimizer: Postgres query optimizer
(11 rows)

explain(locus, costs off) select * from pg_class where oid in (select x-95 from mrs_t1) or oid < 5;
                     QUERY PLAN                     
----------------------------------------------------
 Seq Scan on pg_class
   Locus: Entry
   Filter: ((hashed SubPlan 1) OR (oid < '5'::oid))
   SubPlan 1
     ->  Gather Motion 3:1  (slice1; segments: 3)
           Locus: Entry
           ->  Seq Scan on mrs_t1
                 Locus: Hashed
 Optimizer: Postgres query optimizer
(9 rows)

prepare t1_count(integer) as select count(*) from t1;
explain(locus, costs off) execute t1_count(1);
                   QUERY PLAN                   
------------------------------------------------
 Aggregate
   Locus: NULL
   ->  Gather Motion 3:1  (slice1; segments: 3)
         Locus: NULL
         ->  Seq Scan on t1
               Locus: NULL
 Optimizer: Postgres query optimizer
(7 rows)

explain(costs off, locus) select max(100) from t1;
                        QUERY PLAN                        
----------------------------------------------------------
 Result
   Locus: Entry
   InitPlan 1 (returns $0)  (slice1)
     ->  Limit
           Locus: NULL
           ->  Gather Motion 3:1  (slice2; segments: 3)
                 Locus: Entry
                 ->  Result
                       Locus: Hashed
                       One-Time Filter: (100 IS NOT NULL)
                       ->  Seq Scan on t1
                             Locus: NULL
 Optimizer: Postgres query optimizer
(13 rows)

Fix materialize locus is null when enable_material is off. When creating plan, make_material() is added directly besides a material path and lacks of locus info.
Add locus info for that material plan.

Fix locus is null under Subplan.
fix_subplan_motion() will add Motion by Flow, either Gather or Broadcast. Add locus according to Flow type.

Fix Result, One-Time Filter Result locus is null.
Result node will call create_scan_plan() itself if it's a simple RTE_RESULT base relation. Add locus for that.

Fix PREPARE EXECUTE statement locus null.
Plancache will copy PlannedStmt list if it's not a oneshot plan. Add files locustype and parallel in CopyPlanFields().

Authored-by: Zhang Mingli avamingli@gmail.com

closes: #ISSUE_Number

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LGTM