Allow HOT for BRIN indexed columns.

[simi]

How to test?

CREATE TABLE mytable (             
   id  integer PRIMARY KEY,        
   val integer NOT NULL            
) WITH (autovacuum_enabled = off, fillfactor = 70); 

INSERT INTO mytable SELECT *, 0 FROM generate_series(1, 235);
CREATE INDEX val_brin ON mytable using brin(val);
UPDATE mytable SET val = -3 WHERE id = 42;

SELECT pg_sleep(1); /* pg_stat_user_tables is not immediately updated */

SELECT n_tup_upd, n_tup_hot_upd                                                            
FROM pg_stat_user_tables
WHERE schemaname = 'public'
  AND relname = 'mytable';

/* with this patch */
 n_tup_upd | n_tup_hot_upd 
-----------+---------------
         1 |             1

/* on master */
 n_tup_upd | n_tup_hot_upd 
-----------+---------------
         1 |             0

TODO

• INDEX_ATTR_BITMAP_ALL is used only for HOT decision and since it is not used anymore, it could be removed 🤔