Reformat some node comments

Use per-field comments for IndexInfo, instead of one big header
comment listing all the fields.  This makes the relevant comments
easier to find, and it will also make it less likely that comments are
not updated when fields are added or removed, as has happened in the
past.

Author: Japin Li <japinli@hotmail.com>
Discussion: https://www.postgresql.org/message-id/flat/ME0P300MB04453E6C7EA635F0ECF41BFCB6832%40ME0P300MB0445.AUSP300.PROD.OUTLOOK.COM

src/include/nodes/execnodes.h

@@ -157,35 +157,6 @@ typedef struct ExprState
  *		entries for a particular index.  Used for both index_build and
  *		retail creation of index entries.
  *
- *		NumIndexAttrs		total number of columns in this index
- *		NumIndexKeyAttrs	number of key columns in index
- *		IndexAttrNumbers	underlying-rel attribute numbers used as keys
- *							(zeroes indicate expressions). It also contains
- * 							info about included columns.
- *		Expressions			expr trees for expression entries, or NIL if none
- *		ExpressionsState	exec state for expressions, or NIL if none
- *		Predicate			partial-index predicate, or NIL if none
- *		PredicateState		exec state for predicate, or NIL if none
- *		ExclusionOps		Per-column exclusion operators, or NULL if none
- *		ExclusionProcs		Underlying function OIDs for ExclusionOps
- *		ExclusionStrats		Opclass strategy numbers for ExclusionOps
- *		UniqueOps			These are like Exclusion*, but for unique indexes
- *		UniqueProcs
- *		UniqueStrats
- *		Unique				is it a unique index?
- *		NullsNotDistinct	is NULLS NOT DISTINCT?
- *		ReadyForInserts		is it valid for inserts?
- *		CheckedUnchanged	IndexUnchanged status determined yet?
- *		IndexUnchanged		aminsert hint, cached for retail inserts
- *		Concurrent			are we doing a concurrent index build?
- *		BrokenHotChain		did we detect any broken HOT chains?
- *		WithoutOverlaps		is it a WITHOUT OVERLAPS index?
- *		Summarizing			is it a summarizing index?
- *		ParallelWorkers		# of workers requested (excludes leader)
- *		Am					Oid of index AM
- *		AmCache				private cache area for index AM
- *		Context				memory context holding this IndexInfo
- *
  * ii_Concurrent, ii_BrokenHotChain, and ii_ParallelWorkers are used only
  * during index build; they're conventionally zeroed otherwise.
  * ----------------
@@ -193,31 +164,67 @@ typedef struct ExprState
 typedef struct IndexInfo
 {
 	NodeTag		type;
-	int			ii_NumIndexAttrs;	/* total number of columns in index */
-	int			ii_NumIndexKeyAttrs;	/* number of key columns in index */
+
+	/* total number of columns in index */
+	int			ii_NumIndexAttrs;
+	/* number of key columns in index */
+	int			ii_NumIndexKeyAttrs;
+
+	/*
+	 * Underlying-rel attribute numbers used as keys (zeroes indicate
+	 * expressions). It also contains info about included columns.
+	 */
 	AttrNumber	ii_IndexAttrNumbers[INDEX_MAX_KEYS];
+
+	/* expr trees for expression entries, or NIL if none */
 	List	   *ii_Expressions; /* list of Expr */
+	/* exec state for expressions, or NIL if none */
 	List	   *ii_ExpressionsState;	/* list of ExprState */
+
+	/* partial-index predicate, or NIL if none */
 	List	   *ii_Predicate;	/* list of Expr */
+	/* exec state for expressions, or NIL if none */
 	ExprState  *ii_PredicateState;
+
+	/* Per-column exclusion operators, or NULL if none */
 	Oid		   *ii_ExclusionOps;	/* array with one entry per column */
+	/* Underlying function OIDs for ExclusionOps */
 	Oid		   *ii_ExclusionProcs;	/* array with one entry per column */
+	/* Opclass strategy numbers for ExclusionOps */
 	uint16	   *ii_ExclusionStrats; /* array with one entry per column */
+
+	/* These are like Exclusion*, but for unique indexes */
 	Oid		   *ii_UniqueOps;	/* array with one entry per column */
 	Oid		   *ii_UniqueProcs; /* array with one entry per column */
 	uint16	   *ii_UniqueStrats;	/* array with one entry per column */
+
+	/* is it a unique index? */
 	bool		ii_Unique;
+	/* is NULLS NOT DISTINCT? */
 	bool		ii_NullsNotDistinct;
+	/* is it valid for inserts? */
 	bool		ii_ReadyForInserts;
+	/* IndexUnchanged status determined yet? */
 	bool		ii_CheckedUnchanged;
+	/* aminsert hint, cached for retail inserts */
 	bool		ii_IndexUnchanged;
+	/* are we doing a concurrent index build? */
 	bool		ii_Concurrent;
+	/* did we detect any broken HOT chains? */
 	bool		ii_BrokenHotChain;
+	/* is it a summarizing index? */
 	bool		ii_Summarizing;
+	/* is it a WITHOUT OVERLAPS index? */
 	bool		ii_WithoutOverlaps;
+	/* # of workers requested (excludes leader) */
 	int			ii_ParallelWorkers;
+
+	/* Oid of index AM */
 	Oid			ii_Am;
+	/* private cache area for index AM */
 	void	   *ii_AmCache;
+
+	/* memory context holding this IndexInfo */
 	MemoryContext ii_Context;
 } IndexInfo;