Eliminate some more O(N^2) behaviors in pg_dump/pg_restore.

This patch fixes three places (which AFAICT is all of them) where runtime
was O(N^2) in the number of TOC entries, by using an index array to replace
linear searches of the TOC list.  This performance issue is a bit less bad
than those recently fixed, because it depends on the number of items dumped
not the number in the source database, so the problem can be dodged by
doing partial dumps.

The previous coding already had an instance of one of the two index arrays
needed, but it was only calculated in parallel-restore cases; now we need
it all the time.  I also chose to move the arrays into the ArchiveHandle
data structure, to make this code a bit more ready for the day that we
try to sling multiple ArchiveHandles around in pg_dump or pg_restore.

Since we still need some server-side work before pg_dump can really cope
nicely with tens of thousands of tables, there's probably little point in
back-patching.

src/bin/pg_dump/pg_backup_archiver.h

@@ -251,10 +251,14 @@ typedef struct _archiveHandle
 	void	   *OF;
 	int			gzOut;			/* Output file */
 
-	struct _tocEntry *toc;		/* List of TOC entries */
+	struct _tocEntry *toc;		/* Header of circular list of TOC entries */
 	int			tocCount;		/* Number of TOC entries */
 	DumpId		maxDumpId;		/* largest DumpId among all TOC entries */
 
+	/* arrays created after the TOC list is complete: */
+	struct _tocEntry **tocsByDumpId;		/* TOCs indexed by dumpId */
+	DumpId	   *tableDataId;	/* TABLE DATA ids, indexed by table dumpId */
+
 	struct _tocEntry *currToc;	/* Used when dumping data */
 	int			compression;	/* Compression requested on open Possible
 								 * values for compression: -1