MDEV-19134: EXISTS() slower if ORDER BY is defined

Step 1: Removal of ORDER BY [LIMIT] from the subquery should be done
earlier and for broader class of subqueries.

The rewrite was done in Item_in_subselect::select_in_like_transformer(),
but this had problems:
- It didn't cover EXISTS subqueries
- It covered IN-subqueries, but was done after the semi-join transformation
  was considered inapplicable, because ORDER BY was present.

Remaining issue:
- EXISTS->IN transformation happens before
  check_and_do_in_subquery_rewrites() is called, so it is still prevented
  by the present ORDER BY.

mysql-test/main/subselect_mat_cost_bugs.result

@@ -148,7 +148,7 @@ FROM t2 GROUP BY f1
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
 2	SUBQUERY	t1	system	NULL	NULL	NULL	NULL	1	
-3	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
+3	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using temporary
 drop table t1, t2, t3;
 #
 # LP BUG#715034 Item_sum_distinct::clear(): Assertion `tree != 0' failed