Clean up a few parallelism-related things that pgindent wants to mangle.

In nodeFuncs.c, pgindent wants to introduce spurious indentation into
the definitions of planstate_tree_walker and planstate_walk_subplans.
Fix that by spreading the definition out across several lines, similar
to what is already done for other walker functions in that file.

In execParallel.c, in the definition of SharedExecutorInstrumentation,
pgindent wants to insert more whitespace between the type name and the
member name.  That causes it to mangle comments later on the line.  Fix
by moving the comments out of line.  Now that we have a bit more room,
add some more details that may be useful to the next person reading
this code.

src/backend/executor/execParallel.c

@@ -50,14 +50,29 @@
 
 #define PARALLEL_TUPLE_QUEUE_SIZE		65536
 
-/* DSM structure for accumulating per-PlanState instrumentation. */
+/*
+ * DSM structure for accumulating per-PlanState instrumentation.
+ *
+ * instrument_options: Same meaning here as in instrument.c.
+ *
+ * instrument_offset: Offset, relative to the start of this structure,
+ * of the first Instrumentation object.  This will depend on the length of
+ * the plan_node_id array.
+ *
+ * num_workers: Number of workers.
+ *
+ * num_plan_nodes: Number of plan nodes.
+ *
+ * plan_node_id: Array of plan nodes for which we are gathering instrumentation
+ * from parallel workers.  The length of this array is given by num_plan_nodes.
+ */
 struct SharedExecutorInstrumentation
 {
-	int instrument_options;
-	int instrument_offset;		/* offset of first Instrumentation struct */
-	int num_workers;							/* # of workers */
-	int num_plan_nodes;							/* # of plan nodes */
-	int plan_node_id[FLEXIBLE_ARRAY_MEMBER];	/* array of plan node IDs */
+	int			instrument_options;
+	int			instrument_offset;
+	int			num_workers;
+	int			num_plan_nodes;
+	int			plan_node_id[FLEXIBLE_ARRAY_MEMBER];
 	/* array of num_plan_nodes * num_workers Instrumentation objects follows */
 };
 #define GetInstrumentationArray(sei) \

src/backend/nodes/nodeFuncs.c

@@ -3425,7 +3425,9 @@ raw_expression_tree_walker(Node *node,
  * recurse into any sub-nodes it has.
  */
 bool
-planstate_tree_walker(PlanState *planstate, bool (*walker) (), void *context)
+planstate_tree_walker(PlanState *planstate,
+					  bool (*walker) (),
+					  void *context)
 {
 	Plan	   *plan = planstate->plan;
 	ListCell   *lc;
@@ -3507,7 +3509,9 @@ planstate_tree_walker(PlanState *planstate, bool (*walker) (), void *context)
  * Walk a list of SubPlans (or initPlans, which also use SubPlan nodes).
  */
 static bool
-planstate_walk_subplans(List *plans, bool (*walker) (), void *context)
+planstate_walk_subplans(List *plans,
+						bool (*walker) (),
+						void *context)
 {
 	ListCell   *lc;