sql: column ordinal position mismatch in information_schema.columns after dropping a column

[yuzefovich]

@nvanbenschoten while reviewing #39785 noticed that there is a mismatch between information_schema.columns.ordinal_position and pg_catalog.pg_attribute.attnum after a column has been dropped. This should be fixed. Here is the relevant repro:
In Postgres:

nathan=# drop table if exists hcp_test;
DROP TABLE
nathan=# create table hcp_test(a int, b int, c int);
CREATE TABLE
nathan=# select attname, attnum from pg_attribute where attrelid = 'hcp_test'::regclass;
 attname  | attnum
----------+--------
 tableoid |     -7
 cmax     |     -6
 xmax     |     -5
 cmin     |     -4
 xmin     |     -3
 ctid     |     -1
 a        |      1
 b        |      2
 c        |      3
(9 rows)

nathan=# SELECT column_name, ordinal_position from information_schema.columns where table_name = 'hcp_test';
 column_name | ordinal_position
-------------+------------------
 a           |                1
 b           |                2
 c           |                3
(3 rows)

nathan=# alter table hcp_test drop column b;
ALTER TABLE
nathan=# select attname, attnum from pg_attribute where attrelid = 'hcp_test'::regclass;
           attname            | attnum
------------------------------+--------
 tableoid                     |     -7
 cmax                         |     -6
 xmax                         |     -5
 cmin                         |     -4
 xmin                         |     -3
 ctid                         |     -1
 a                            |      1
 ........pg.dropped.2........ |      2
 c                            |      3
(9 rows)

nathan=# SELECT column_name, ordinal_position from information_schema.columns where table_name = 'hcp_test';
 column_name | ordinal_position
-------------+------------------
 a           |                1
 c           |                3
(2 rows)

In CockroachDB:

root@127.0.0.1:58308/movr> drop table if exists hcp_test;
DROP TABLE
root@127.0.0.1:58308/movr> create table hcp_test(a int, b int, c int);
CREATE TABLE
root@127.0.0.1:58308/movr> select attname, attnum from pg_attribute where attrelid = 'hcp_test'::regclass;
  attname | attnum
+---------+--------+
  a       |      1
  b       |      2
  c       |      3
  rowid   |      4
(4 rows)
root@127.0.0.1:58308/movr> SELECT column_name, ordinal_position from information_schema.columns where table_name = 'hcp_test';
  column_name | ordinal_position
+-------------+------------------+
  a           |                1
  b           |                2
  c           |                3
  rowid       |                4
(4 rows)
root@127.0.0.1:58308/movr> alter table hcp_test drop column b;
ALTER TABLE
root@127.0.0.1:58308/movr> select attname, attnum from pg_attribute where attrelid = 'hcp_test'::regclass;
  attname | attnum
+---------+--------+
  a       |      1
  c       |      3
  rowid   |      4
(3 rows)
root@127.0.0.1:58308/movr> SELECT column_name, ordinal_position from information_schema.columns where table_name = 'hcp_test';
  column_name | ordinal_position
+-------------+------------------+
  a           |                1
  c           |                2
  rowid       |                3
(3 rows)