Add ALTER EXTENSION ADD/DROP ACCESS METHOD, and use it in pg_upgrade.

Without this, an extension containing an access method is not properly
dumped/restored during pg_upgrade --- the AM ends up not being a member
of the extension after upgrading.

Another oversight in commit 473b9328, reported by Andrew Dunstan.

Report: <f7ac29f3-515c-2a44-21c5-ec925053265f@dunslane.net>

doc/src/sgml/ref/alter_extension.sgml

@@ -30,6 +30,7 @@ ALTER EXTENSION <replaceable class="PARAMETER">name</replaceable> DROP <replacea
 
 <phrase>where <replaceable class="PARAMETER">member_object</replaceable> is:</phrase>
 
+  ACCESS METHOD <replaceable class="PARAMETER">object_name</replaceable> |
   AGGREGATE <replaceable class="PARAMETER">aggregate_name</replaceable> ( <replaceable>aggregate_signature</replaceable> ) |
   CAST (<replaceable>source_type</replaceable> AS <replaceable>target_type</replaceable>) |
   COLLATION <replaceable class="PARAMETER">object_name</replaceable> |

src/backend/parser/gram.y

@@ -3931,7 +3931,16 @@ alter_extension_opt_item:
  *****************************************************************************/
 
 AlterExtensionContentsStmt:
-			ALTER EXTENSION name add_drop AGGREGATE func_name aggr_args
+			ALTER EXTENSION name add_drop ACCESS METHOD name
+				{
+					AlterExtensionContentsStmt *n = makeNode(AlterExtensionContentsStmt);
+					n->extname = $3;
+					n->action = $4;
+					n->objtype = OBJECT_ACCESS_METHOD;
+					n->objname = list_make1(makeString($7));
+					$$ = (Node *)n;
+				}
+			| ALTER EXTENSION name add_drop AGGREGATE func_name aggr_args
 				{
 					AlterExtensionContentsStmt *n = makeNode(AlterExtensionContentsStmt);
 					n->extname = $3;

src/bin/pg_dump/pg_dump.c

@@ -12505,6 +12505,9 @@ dumpAccessMethod(Archive *fout, AccessMethodInfo *aminfo)
 	appendPQExpBuffer(labelq, "ACCESS METHOD %s",
 					  qamname);
 
+	if (dopt->binary_upgrade)
+		binary_upgrade_extension_member(q, &aminfo->dobj, labelq->data);
+
 	if (aminfo->dobj.dump & DUMP_COMPONENT_DEFINITION)
 		ArchiveEntry(fout, aminfo->dobj.catId, aminfo->dobj.dumpId,
 					 aminfo->dobj.name,