Ensure stored generated columns must be published when required.

Ensure stored generated columns that are part of REPLICA IDENTITY must be
published explicitly for UPDATE and DELETE operations to be published. We
can publish generated columns by listing them in the column list or by
enabling the publish_generated_columns option.

This commit changes the behavior of the test added in commit adedf54e65 by
giving an ERROR for the UPDATE operation in such cases. There is no way to
trigger the bug reported in commit adedf54e65 but we didn't remove the
corresponding code change because it is still relevant when replicating
changes from a publisher with version less than 18.

We decided not to backpatch this behavior change to avoid the risk of
breaking existing output plugins that may be sending generated columns by
default although we are not aware of any such plugin. Also, we didn't see
any reports related to this on STABLE branches which is another reason not
to backpatch this change.

Author: Shlok Kyal, Hou Zhijie
Reviewed-by: Vignesh C, Amit Kapila
Discussion: https://postgr.es/m/CANhcyEVw4V2Awe2AB6i0E5AJLNdASShGfdBLbUd1XtWDboymCA@mail.gmail.com

doc/src/sgml/ref/create_publication.sgml

@@ -311,6 +311,14 @@ CREATE PUBLICATION <replaceable class="parameter">name</replaceable>
    system columns.
   </para>
 
+  <para>
+   The generated columns that are part of <literal>REPLICA IDENTITY</literal>
+   must be published explicitly either by listing them in the column list or
+   by enabling the <literal>publish_generated_columns</literal> option, in
+   order for <command>UPDATE</command> and <command>DELETE</command> operations
+   to be published.
+  </para>
+
   <para>
    The row filter on a table becomes redundant if
    <literal>FOR TABLES IN SCHEMA</literal> is specified and the table