MDEV-30218: Incorrect optimization for rowid_filtering

(Patch from Monty, slightly amended)

Fix rowid filtering optimization in best_access_path():

== Ref access + rowid filtering ==
The cost computations compare #records and index-only scan cost
(keyread_tmp) to find out the per-record advantage one will get if
they skip reading full table record.

The computations produce wrong result when:

- the #records are "clipped down" with s->worst_seeks or
  thd->variables.max_seeks_for_key. keyread_tmp is not clipped
  this way so the numbers are not comparable.

- access_factor is negative. This means index_only read is
  cheaper than non-index-only read.

This patch makes the optimizer not to consider Rowid Filtering in
such cases.
The decision is logged in the Optimizer Trace using
"rowid_filter_skipped" name.

== Range access + rowid filtering ==
when considering to use Rowid Filter with range access, do multiply
keyread_tmp by record_count. That way, it is comparable with the
range access's estimate, which is multiplied by record_count.

mysql-test/main/selectivity_innodb.result

@@ -1671,7 +1671,7 @@ Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1`
 # gives selectivity data
 explain extended select * from t1 where a in (17,51,5) and b=2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	ref|filter	b,a	b|a	5|5	const	59 (3%)	2.90	Using where; Using rowid filter
+1	SIMPLE	t1	ref	b,a	b	5	const	59	2.90	Using where
 Warnings:
 Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where `test`.`t1`.`b` = 2 and `test`.`t1`.`a` in (17,51,5)
 drop table t1;