Extend object-access hook machinery to support post-alter events.

This also slightly widens the scope of what we support in terms of
post-create events.

KaiGai Kohei, with a few changes, mostly to the comments, by me

src/backend/catalog/pg_db_role_setting.c

@@ -14,6 +14,7 @@
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "catalog/indexing.h"
+#include "catalog/objectaccess.h"
 #include "catalog/pg_db_role_setting.h"
 #include "utils/fmgroids.h"
 #include "utils/rel.h"
@@ -160,6 +161,9 @@ AlterSetting(Oid databaseid, Oid roleid, VariableSetStmt *setstmt)
 		CatalogUpdateIndexes(rel, newtuple);
 	}
 
+	InvokeObjectPostAlterHookArg(DbRoleSettingRelationId,
+								 databaseid, 0, roleid, false);
+
 	systable_endscan(scan);
 
 	/* Close pg_db_role_setting, but keep lock till commit */