Expand OAT_POST_{CREATE,ALTER} handling

Also remove corresponding NodeTags from the ProcessUtility_hook's
"only if no event triggers" section.

Note that both materialized views and "CREATE TABLE ... AS ..." statements
generate events handled by log_create_or_alter(), also
"CREATE MATERIALIZED VIEW" actually has node type T_CreateTableAsStmt,
so T_CreateTableAsStmt removed as well.