Removed double records_in_range calls from multi_range_read_info_const

This was to remove a performance regression between 10.3 and 10.4
In 10.5 we will have a better implementation of records_in_range
that will enable us to get more statistics.
This change was not done in 10.4 because the 10.5 will be part of
a larger change that is not suitable for the GA 10.4 version

Other things:
- Changed default handler block_size to 8192 to fix things statistics
  for engines that doesn't set the block size.
- Fixed a bug in spider when using multiple part const ranges
  (Patch from Kentoku)

storage/rocksdb/mysql-test/rocksdb/r/index_merge_rocksdb2.result

@@ -479,7 +479,7 @@ a	filler	b
 must use union, not sort-union:
 explain select * from t2 where a=4 or b=4;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t2	ALL	a,b	NULL	NULL	NULL	#	Using where
+1	SIMPLE	t2	index_merge	a,b	a,b	5,5	NULL	#	Using union(a,b); Using where
 select * from t2 where a=4 or b=4;
 a	filler	b
 4	4	0

storage/rocksdb/mysql-test/rocksdb/r/type_char_indexes.result

@@ -45,7 +45,7 @@ t1	1	v16	1	v16	A	500	NULL	NULL	YES	LSMTREE
 INSERT INTO t1 (c,c20,v16,v128,pk) VALUES ('a','char1','varchar1a','varchar1b','1'),('a','char2','varchar2a','varchar2b','2'),('b','char3','varchar1a','varchar1b','3'),('c','char4','varchar3a','varchar3b','4');
 EXPLAIN SELECT SUBSTRING(v16,0,3) FROM t1 WHERE v16 LIKE 'varchar%';
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	v16	v16	21	NULL	#	Using where; Using index
+1	SIMPLE	t1	range	v16	v16	19	NULL	#	Using where; Using index
 SELECT SUBSTRING(v16,7,3) FROM t1 WHERE v16 LIKE 'varchar%';
 SUBSTRING(v16,7,3)
 r1a

storage/rocksdb/mysql-test/rocksdb/r/type_date_time_indexes.result

@@ -62,7 +62,7 @@ INSERT INTO t1 (d,dt,ts,t,y,pk) VALUES
 (DATE(@tm),@tm,TIMESTAMP(@tm),TIME(@tm),YEAR(@tm),'12:05:00');
 EXPLAIN SELECT ts FROM t1 WHERE ts > NOW();
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	ts	ts	5	NULL	#	Using where; Using index
+1	SIMPLE	t1	range	ts	ts	5	NULL	#	Using where; Using index
 SELECT ts FROM t1 WHERE ts > NOW();
 ts
 EXPLAIN SELECT ts FROM t1 USE INDEX () WHERE ts > NOW();