MDEV-30699: Updated prev_record_reads() to be more exact

The old code in prev_record_reads() did give wrong estimates when a
join_buffer was used or if the table was depending on more than one
other tables. When join_cache is used, it will cause a re-order of row
combinations, which causes more calls to the engine for tables that
are depending on tables before the join_cached one.

The new prev_records_read() code provides more exact estimates and
should never give a 'too low estimate', assuming that the data to the
function is correct

The definition of prev_record_read() is also updated.
The new definition is:
  "Estimate the number of engine ha_index_read_calls for EQ_REF tables
  when taking into account the one-row-cache in join_read_always_key()"

The cost of using prev_record_reads() value is changed. The value is
now used similar as before to calculate the cost of the storage engine
calls. However the cost of the WHERE cost is changed to take into
account the total number of row combinations as the WHERE has to be
checked even if the one-row-cache is used. This makes the cost
slightly higher than before (for the same prev_record_reads() value).

Other things:
- Cached return value of prev_record_read() in best_access_path() to
  avoid some function calls.
- Fixed bug where position[].use_join_buffer was set in
  best_acess_path() when join buffer was not used. This confused the
  semi join optimizer to try to reoptimize plans that did not need to be
  reoptimized.
  The effect of the bug fix is that we avoid doing some re-optimziations
  with semi-joins when join_buffer is not used. In these cases the value
  shown for the 'Filtering' column in EXPLAIN EXTENDED may change.
- Added 'prev_record.cc' that was used to verify the logic in
  prev_record_reads().

Changes in test suite:
- EQ_REF tables are moved up to be earlier. This is because either the
  higher WHERE cost when EQ_REF is used with more row combination or
  change of cost when using join_cache.
- Filtered has changed (to the better) for some cases using semi-joins
  subselect_sj.test subselect_sj_jcl6.test

mysql-test/main/subselect2.result

@@ -125,8 +125,8 @@ DOCID	DOCNAME	DOCTYPEID	FOLDERID	AUTHOR	CREATED	TITLE	SUBTITLE	DOCABSTRACT	PUBLI
 c373e9f5ad07993f3859444553544200	Last Discussion	c373e9f5ad079174ff17444553544200	c373e9f5ad0796c0eca4444553544200	Goldilocks	2003-06-09 11:21:06	Title: Last Discussion	NULL	Setting new abstract and keeping doc checked out	2003-06-09 10:51:26	2003-06-09 10:51:26	NULL	NULL	NULL	03eea05112b845949f3fd03278b5fe43	2003-06-09 11:21:06	admin	0	NULL	Discussion	NULL	NULL
 EXPLAIN SELECT t2.*, t4.DOCTYPENAME, t1.CONTENTSIZE,t1.MIMETYPE FROM t2 INNER JOIN t4 ON t2.DOCTYPEID = t4.DOCTYPEID LEFT OUTER JOIN t1 ON t2.DOCID = t1.DOCID WHERE t2.FOLDERID IN(SELECT t3_a.FOLDERID FROM t3 as t3_a WHERE t3_a.PARENTID IN(SELECT t3_b.FOLDERID FROM t3 as t3_b WHERE t3_b.PARENTID IN(SELECT t3_c.FOLDERID FROM t3 as t3_c WHERE t3_c.PARENTID IN(SELECT t3_d.FOLDERID FROM t3 as t3_d WHERE t3_d.PARENTID IN(SELECT t3_e.FOLDERID FROM t3 as t3_e WHERE t3_e.PARENTID='2f6161e879db43c1a5b82c21ddc49089' AND t3_e.FOLDERNAME = 'Level1') AND t3_d.FOLDERNAME = 'Level2') AND t3_c.FOLDERNAME = 'Level3') AND t3_b.FOLDERNAME = 'CopiedFolder') AND t3_a.FOLDERNAME = 'Movie Reviews') AND t2.DOCNAME = 'Last Discussion';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t4	ALL	PRIMARY	NULL	NULL	NULL	10	
-1	PRIMARY	t2	ALL	DDOCTYPEID_IDX,DFOLDERID_IDX	NULL	NULL	NULL	9	Using where; Using join buffer (flat, BNL join)
+1	PRIMARY	t2	ALL	DDOCTYPEID_IDX,DFOLDERID_IDX	NULL	NULL	NULL	9	Using where
+1	PRIMARY	t4	eq_ref	PRIMARY	PRIMARY	34	test.t2.DOCTYPEID	1	
 1	PRIMARY	t1	eq_ref	PRIMARY	PRIMARY	34	test.t2.DOCID	1	
 1	PRIMARY	t3_a	eq_ref	PRIMARY,FFOLDERID_IDX,CMFLDRPARNT_IDX	PRIMARY	34	test.t2.FOLDERID	1	Using where
 1	PRIMARY	t3_b	eq_ref	PRIMARY,FFOLDERID_IDX,CMFLDRPARNT_IDX	PRIMARY	34	test.t3_a.PARENTID	1	Using where