Generate translator comments for GUC parameter descriptions

Automatically generate comments like

    /* translator: GUC parameter "client_min_messages" short description */

in the generated guc_tables.inc.c.

This provides translators more context.

Reviewed-by: Pavlo Golub <pavlo.golub@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Stéphane Schildknecht <sas.postgresql@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/1a89b3f0-e588-41ef-b712-aba766143cad%40eisentraut.org

src/backend/utils/misc/gen_guc_tables.pl

@@ -110,11 +110,20 @@ sub print_table
 		printf $ofh "\t\t.name = %s,\n", dquote($entry->{name});
 		printf $ofh "\t\t.context = %s,\n", $entry->{context};
 		printf $ofh "\t\t.group = %s,\n", $entry->{group};
+		printf $ofh
+		  "\t\t/* translator: GUC parameter \"%s\" short description */\n",
+		  $entry->{name};
 		printf $ofh "\t\t.short_desc = gettext_noop(%s),\n",
 		  dquote($entry->{short_desc});
+
+		if ($entry->{long_desc})
+		{
+			printf $ofh
+			  "\t\t/* translator: GUC parameter \"%s\" long description */\n",
+			  $entry->{name};
 			printf $ofh "\t\t.long_desc = gettext_noop(%s),\n",
-		  dquote($entry->{long_desc})
-		  if $entry->{long_desc};
+			  dquote($entry->{long_desc});
+		}
 		printf $ofh "\t\t.flags = %s,\n", $entry->{flags} if $entry->{flags};
 		printf $ofh "\t\t.vartype = %s,\n", ('PGC_' . uc($entry->{type}));
 		printf $ofh "\t\t._%s = {\n", $entry->{type};