Reformat some node comments
Reformat some comments in node field definitions to avoid long lines.
This makes room for per-field annotations. Similar to
835d476fd2.
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://www.postgresql.org/message-id/flat/
4b27fc50-8cd6-46f5-ab20-
88dbaadca645@eisentraut.org