Added EQ_REF chaining to the greedy_optimizer

MDEV-28073 Slow query performance in MariaDB when using many table

The idea is to prefer and chain EQ_REF tables (tables that uses an
unique key to find a row) when searching for the best table combination.
This significantly reduces row combinations that has to be examined.
This is optimization is enabled when setting optimizer_prune_level=2
(which is now default).

Implementation:
- optimizer_prune_level has a new level, 2, which enables EQ_REF
  optimization in addition to the pruning done by level 1.
  Level 2 is now default.
- Added JOIN::eq_ref_tables that contains bits of tables that could use
  potentially use EQ_REF access in the query.  This is calculated
  in sort_and_filter_keyuse()

Under optimizer_prune_level=2:
- When the greedy_optimizer notices that the preceding table was an
  EQ_REF table, it tries to add an EQ_REF table next. If an EQ_REF
  table exists, only this one will be considered at this level.
  We also collect all EQ_REF tables chained by the next levels and these
  are ignored on the starting level as we have already examined these.
  If no EQ_REF table exists, we continue as normal.

This optimization speeds up the greedy_optimizer combination test with
~25%

Other things:
- I ported the changes in MySQL 5.7 to greedy_optimizer.test to MariaDB
  to be able to ensure we can handle all cases that MySQL can do.
- I have run all tests with --mysqld=--optimizer_prune_level=1 to verify that
  there where no test changes.

mysql-test/main/stat_tables_innodb.result

@@ -248,10 +248,10 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	part	ALL	PRIMARY	NULL	NULL	NULL	200	Using where; Using join buffer (flat, BNL join)
 1	SIMPLE	lineitem	ref	PRIMARY,i_l_suppkey_partkey,i_l_partkey,i_l_suppkey,i_l_orderkey,i_l_orderkey_quantity	i_l_partkey	5	dbt3_s001.part.p_partkey	30	Using where
 1	SIMPLE	supplier	eq_ref	PRIMARY,i_s_nationkey	PRIMARY	4	dbt3_s001.lineitem.l_suppkey	1	Using where
+1	SIMPLE	n2	eq_ref	PRIMARY	PRIMARY	4	dbt3_s001.supplier.s_nationkey	1	
 1	SIMPLE	orders	eq_ref	PRIMARY,i_o_orderdate,i_o_custkey	PRIMARY	4	dbt3_s001.lineitem.l_orderkey	1	Using where
 1	SIMPLE	customer	eq_ref	PRIMARY,i_c_nationkey	PRIMARY	4	dbt3_s001.orders.o_custkey	1	Using where
 1	SIMPLE	n1	eq_ref	PRIMARY,i_n_regionkey	PRIMARY	4	dbt3_s001.customer.c_nationkey	1	Using where
-1	SIMPLE	n2	eq_ref	PRIMARY	PRIMARY	4	dbt3_s001.supplier.s_nationkey	1	
 select o_year,
 sum(case when nation = 'UNITED STATES' then volume else 0 end) /
 sum(volume) as mkt_share