Add missing invocations to object access hooks

The following commands have been missing calls to object access hooks
InvokeObjectPost{Create|Alter}Hook normally applied to all commands:
- ALTER RULE RENAME TO
- ALTER USER MAPPING
- CREATE ACCESS METHOD
- CREATE STATISTICS

Thanks also to Robert Haas for the discussion.

Author: Mark Dilger
Reviewed-by: Álvaro Herrera, Michael Paquier
Discussion: https://postgr.es/m/435CD295-F409-44E0-91EC-DF32C7AFCD76@enterprisedb.com

src/backend/commands/statscmds.c

@@ -374,6 +374,8 @@ CreateStatistics(CreateStatsStmt *stmt)
 
 	relation_close(datarel, RowExclusiveLock);
 
+	InvokeObjectPostCreateHook(StatisticExtRelationId, statoid, 0);
+
 	/*
 	 * Invalidate relcache so that others see the new statistics object.
 	 */