Adapt "Right Semi Join" backport for Apache Cloudberry MPP

This commit carries the Cloudberry/Greenplum-specific changes needed on
top of the two cherry-picked upstream commits (aa86129, 5668a85),
which only touch the upstream PostgreSQL planner/executor files.

- nodes.h: move JOIN_RIGHT_SEMI to the END of the JoinType enum. Upstream
  places it next to JOIN_RIGHT_ANTI, but in the Cloudberry tree that shifts
  the integer values of the GPDB-specific JOIN_DEDUP_SEMI/REVERSE and
  JOIN_UNIQUE_* codes. Value-dependent code then corrupts MPP motion
  planning, producing a degenerate plan ("Gather Motion 0:1" /
  "Redistribute Motion 1:0") that crashes with SIGSEGV in
  setupCdbProcessList() during dispatch. Appending keeps every pre-existing
  enum value stable.

- cdbpath.c (cdbpath_motion_for_join, both the serial and parallel switch):
  handle JOIN_RIGHT_SEMI like JOIN_RIGHT/JOIN_RIGHT_ANTI. A right-semi join
  emits inner (build-side) rows, so the inner side must not be replicated,
  otherwise matched inner rows could be emitted more than once. Without this
  the new join type would hit the switch default and elog(ERROR,
  "unexpected join type") at plan time.

Note: this feature is only exercised by the PostgreSQL planner
(optimizer=off); GPORCA does not generate JOIN_RIGHT_SEMI.

Author: kongfanshen

src/backend/cdb/cdbpath.c

@@ -1469,7 +1469,13 @@ cdbpath_motion_for_join(PlannerInfo *root,
 			outer.ok_to_replicate = false;
 			break;
 		case JOIN_RIGHT:
+		case JOIN_RIGHT_SEMI:
 		case JOIN_RIGHT_ANTI:
+			/*
+			 * GPDB: A right-semi join emits inner (build-side) rows, so just
+			 * like JOIN_RIGHT/JOIN_RIGHT_ANTI the inner side must not be
+			 * replicated, or matched inner rows could be emitted more than once.
+			 */
 			inner.ok_to_replicate = false;
 			break;
 		case JOIN_FULL:
@@ -3220,6 +3226,7 @@ cdbpath_motion_for_parallel_join(PlannerInfo *root,
 		case JOIN_UNIQUE_OUTER:
 		case JOIN_UNIQUE_INNER:
 		case JOIN_RIGHT:
+		case JOIN_RIGHT_SEMI:
 		case JOIN_RIGHT_ANTI:
 		case JOIN_FULL:
 			outer.ok_to_replicate = false;

src/include/nodes/nodes.h

@@ -1026,7 +1026,6 @@ typedef enum JoinType
 	JOIN_LASJ_NOTIN,			/* Left Anti Semi Join with Not-In semantics:
 									If any NULL values are produced by inner side,
 									return no join results. Otherwise, same as LASJ */
-	JOIN_RIGHT_SEMI,			/* 1 copy of each RHS row that has match(es) */
 	JOIN_RIGHT_ANTI,			/* 1 copy of each RHS row that has no match */
 
 	/*
@@ -1046,7 +1045,19 @@ typedef enum JoinType
 	 * moving the larger of the two relations.
 	 */
 	JOIN_DEDUP_SEMI,			/* inner join, LHS path must be made unique afterwards */
-	JOIN_DEDUP_SEMI_REVERSE		/* inner join, RHS path must be made unique afterwards */
+	JOIN_DEDUP_SEMI_REVERSE,	/* inner join, RHS path must be made unique afterwards */
+
+	/*
+	 * JOIN_RIGHT_SEMI (backported from upstream commit aa86129e1) is an
+	 * executor-supported join type, but it is deliberately placed at the END
+	 * of this enum rather than next to JOIN_RIGHT_ANTI where upstream puts it.
+	 * Inserting it in the middle would shift the integer values of the
+	 * GPDB-specific JOIN_DEDUP_SEMI/REVERSE (and JOIN_UNIQUE_*) codes, which
+	 * breaks value-dependent code elsewhere and corrupts MPP motion planning
+	 * (observed as a SIGSEGV during dispatch on semijoins over non-partitioned
+	 * loci).  Appending here keeps every pre-existing value stable.
+	 */
+	JOIN_RIGHT_SEMI				/* 1 copy of each RHS row that has match(es) */
 
 	/*
 	 * We might need additional join types someday.