In INSERT/UPDATE, use the table's real tuple descriptor as target.

This back-patches commit 20d3fe90 into the v12 and v13 branches.
At the time I thought that commit was not fixing any observable
bug, but Bertrand Drouvot showed otherwise: adding a dropped column
to the previously-considered scenario crashes v12 and v13, unless the
dropped column happens to be an integer.  That is, of course, because
the tupdesc we derive from the plan output tlist fails to describe
the dropped column accurately, so that we'll do the wrong thing with
a tuple in which that column isn't NULL.

There is no bug in pre-v12 branches because they already did use
the table's real tuple descriptor for any trigger-returned tuple.
It seems that this set of bugs can be blamed on the changes that
removed es_trig_tuple_slot, though I've not attempted to pin that
down precisely.

Although there's no code change needed in HEAD, update the test case
to include a dropped column there too.

Discussion: https://postgr.es/m/db5d97c8-f48a-51e2-7b08-b73d5434d425@amazon.com
Discussion: https://postgr.es/m/16644-5da7ef98a7ac4545@postgresql.org

src/test/regress/expected/triggers.out

@@ -216,34 +216,56 @@ select * from trigtest;
 
 drop table trigtest;
 -- Check behavior with an implicit column default, too (bug #16644)
-create table trigtest (a integer);
+create table trigtest (
+  a integer,
+  b bool default true not null,
+  c text default 'xyzzy' not null);
 create trigger trigger_return_old
 	before insert or delete or update on trigtest
 	for each row execute procedure trigger_return_old();
 insert into trigtest values(1);
 select * from trigtest;
- a 
----
- 1
+ a | b |   c   
+---+---+-------
+ 1 | t | xyzzy
+(1 row)
+
+alter table trigtest add column d integer default 42 not null;
+select * from trigtest;
+ a | b |   c   | d  
+---+---+-------+----
+ 1 | t | xyzzy | 42
+(1 row)
+
+update trigtest set a = 2 where a = 1 returning *;
+ a | b |   c   | d  
+---+---+-------+----
+ 1 | t | xyzzy | 42
+(1 row)
+
+select * from trigtest;
+ a | b |   c   | d  
+---+---+-------+----
+ 1 | t | xyzzy | 42
 (1 row)
 
-alter table trigtest add column b integer default 42 not null;
+alter table trigtest drop column b;
 select * from trigtest;
- a | b  
----+----
- 1 | 42
+ a |   c   | d  
+---+-------+----
+ 1 | xyzzy | 42
 (1 row)
 
 update trigtest set a = 2 where a = 1 returning *;
- a | b  
----+----
- 1 | 42
+ a |   c   | d  
+---+-------+----
+ 1 | xyzzy | 42
 (1 row)
 
 select * from trigtest;
- a | b  
----+----
- 1 | 42
+ a |   c   | d  
+---+-------+----
+ 1 | xyzzy | 42
 (1 row)
 
 drop table trigtest;

src/test/regress/sql/triggers.sql

@@ -155,7 +155,10 @@ select * from trigtest;
 drop table trigtest;
 
 -- Check behavior with an implicit column default, too (bug #16644)
-create table trigtest (a integer);
+create table trigtest (
+  a integer,
+  b bool default true not null,
+  c text default 'xyzzy' not null);
 
 create trigger trigger_return_old
 	before insert or delete or update on trigtest
@@ -164,7 +167,13 @@ create trigger trigger_return_old
 insert into trigtest values(1);
 select * from trigtest;
 
-alter table trigtest add column b integer default 42 not null;
+alter table trigtest add column d integer default 42 not null;
+
+select * from trigtest;
+update trigtest set a = 2 where a = 1 returning *;
+select * from trigtest;
+
+alter table trigtest drop column b;
 
 select * from trigtest;
 update trigtest set a = 2 where a = 1 returning *;