sql: vectorized escapes LIKE '%\\%' incorrectly

[otan]

Describe the problem

LIKE '%\\%'

To Reproduce

This is a problem since v21.1, guessing since vectorize was on by default.

Setup:

 CREATE TABLE public.lookup_article (
      id SERIAL PRIMARY KEY,
      headline VARCHAR(100) NOT NULL,
      pub_date TIMESTAMPTZ NOT NULL,
      author_id INT8 NULL,
      slug VARCHAR(50) NULL
  );
  INSERT INTO "lookup_article" ("headline", "pub_date", "author_id", "slug") VALUES ('Article with \ backslash', '2005-11-22T00:00:00-06:00'::timestamptz, NULL, NULL) RETURNING "lookup_article"."id";

Now observe the difference in results when vectorized is off vs on:

[email protected]:26257/defaultdb> set vectorize=off;
SET


Time: 0ms total (execution 0ms / network 0ms)

[email protected]:26257/defaultdb> SELECT "lookup_article"."id", "lookup_article"."headline", "lookup_article"."pub_date", "lookup_article"."author_id", "lookup_article"."slug" FROM "lookup_article" WHERE "lookup_article"."headline" LIKE '%\\%';
          id         |         headline         |        pub_date        | author_id | slug
---------------------+--------------------------+------------------------+-----------+-------
  678626193848238081 | Article with \ backslash | 2005-11-22 06:00:00+00 |      NULL | NULL
(1 row)


Time: 1ms total (execution 1ms / network 0ms)

[email protected]:26257/defaultdb> set vectorize=on;
SET


Time: 0ms total (execution 0ms / network 0ms)

[email protected]:26257/defaultdb> SELECT "lookup_article"."id", "lookup_article"."headline", "lookup_article"."pub_date", "lookup_article"."author_id", "lookup_article"."slug" FROM "lookup_article" WHERE "lookup_article"."headline" LIKE '%\\%';
  id | headline | pub_date | author_id | slug
-----+----------+----------+-----------+-------
(0 rows)

The vectorize=off result is the expected result.

Found by #67974

[otan]

cc @yuzefovich