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/suite/sys_vars/r/optimizer_prune_level_basic.result

@@ -1,35 +1,35 @@
 SET @start_global_value = @@global.optimizer_prune_level;
 SELECT @start_global_value;
 @start_global_value
-1
+2
 SET @start_session_value = @@session.optimizer_prune_level;
 SELECT @start_session_value;
 @start_session_value
-1
+2
 '#--------------------FN_DYNVARS_115_01-------------------------#'
 SET @@global.optimizer_prune_level = 0;
 SET @@global.optimizer_prune_level = DEFAULT;
 SELECT @@global.optimizer_prune_level;
 @@global.optimizer_prune_level
-1
+2
 SET @@session.optimizer_prune_level = 0;
 SET @@session.optimizer_prune_level = DEFAULT;
 SELECT @@session.optimizer_prune_level;
 @@session.optimizer_prune_level
-1
+2
 '#--------------------FN_DYNVARS_115_02-------------------------#'
 SET @@global.optimizer_prune_level = DEFAULT;
-SELECT @@global.optimizer_prune_level = 1;
-@@global.optimizer_prune_level = 1
+SELECT @@global.optimizer_prune_level = 2;
+@@global.optimizer_prune_level = 2
 1
 SET @@session.optimizer_prune_level = DEFAULT;
-SELECT @@session.optimizer_prune_level = 1;
-@@session.optimizer_prune_level = 1
+SELECT @@session.optimizer_prune_level = 2;
+@@session.optimizer_prune_level = 2
 1
 '#--------------------FN_DYNVARS_115_03-------------------------#'
 SELECT @@global.optimizer_prune_level;
 @@global.optimizer_prune_level
-1
+2
 SET @@global.optimizer_prune_level = 0;
 SELECT @@global.optimizer_prune_level;
 @@global.optimizer_prune_level
@@ -38,6 +38,10 @@ SET @@global.optimizer_prune_level = 1;
 SELECT @@global.optimizer_prune_level;
 @@global.optimizer_prune_level
 1
+SET @@global.optimizer_prune_level = 2;
+SELECT @@global.optimizer_prune_level;
+@@global.optimizer_prune_level
+2
 SET @@global.optimizer_prune_level = TRUE;
 SELECT @@global.optimizer_prune_level;
 @@global.optimizer_prune_level
@@ -49,7 +53,7 @@ SELECT @@global.optimizer_prune_level;
 '#--------------------FN_DYNVARS_115_04-------------------------#'
 SELECT @@session.optimizer_prune_level;
 @@session.optimizer_prune_level
-1
+2
 SET @@session.optimizer_prune_level = 0;
 SELECT @@session.optimizer_prune_level;
 @@session.optimizer_prune_level
@@ -58,6 +62,10 @@ SET @@session.optimizer_prune_level = 1;
 SELECT @@session.optimizer_prune_level;
 @@session.optimizer_prune_level
 1
+SET @@session.optimizer_prune_level = 2;
+SELECT @@session.optimizer_prune_level;
+@@session.optimizer_prune_level
+2
 SET @@session.optimizer_prune_level = TRUE;
 SELECT @@session.optimizer_prune_level;
 @@session.optimizer_prune_level
@@ -69,7 +77,7 @@ SELECT @@session.optimizer_prune_level;
 '#------------------FN_DYNVARS_115_05-----------------------#'
 SET @@global.optimizer_prune_level = ON;
 ERROR 42000: Incorrect argument type to variable 'optimizer_prune_level'
-'Bug# 34840: Since it is a boolean variable, it should not give errors on 'ON' & 'OFF' values';
+'Bug# 34840: Since it is not a boolean variable, it should give errors on 'ON' & 'OFF' values';
 SET @@global.optimizer_prune_level = OFF;
 ERROR 42000: Incorrect argument type to variable 'optimizer_prune_level'
 SET @@global.optimizer_prune_level = 'ONN';
@@ -86,10 +94,16 @@ Warning	1292	Truncated incorrect optimizer_prune_level value: '-1024'
 SELECT @@global.optimizer_prune_level;
 @@global.optimizer_prune_level
 0
-'Bug# 34840: Since it is a boolean variable, it should give errors on numeric values';
+'Bug# 34840: Since it is not a boolean variable, it should no give errors on numeric values';
 SET @@global.optimizer_prune_level = 65536;
 Warnings:
 Warning	1292	Truncated incorrect optimizer_prune_level value: '65536'
+SET @@global.optimizer_prune_level = 3;
+Warnings:
+Warning	1292	Truncated incorrect optimizer_prune_level value: '3'
+select @@global.optimizer_prune_level;
+@@global.optimizer_prune_level
+2
 SET @@global.optimizer_prune_level = 65530.34;
 ERROR 42000: Incorrect argument type to variable 'optimizer_prune_level'
 SET @@global.optimizer_prune_level = test;
@@ -121,7 +135,7 @@ Warnings:
 Warning	1292	Truncated incorrect optimizer_prune_level value: '65550'
 SELECT @@session.optimizer_prune_level;
 @@session.optimizer_prune_level
-1
+2
 SET @@session.optimizer_prune_level = test;
 ERROR 42000: Incorrect argument type to variable 'optimizer_prune_level'
 '#------------------FN_DYNVARS_115_06-----------------------#'
@@ -164,8 +178,8 @@ ERROR 42S22: Unknown column 'optimizer_prune_level' in 'field list'
 SET @@global.optimizer_prune_level = @start_global_value;
 SELECT @@global.optimizer_prune_level;
 @@global.optimizer_prune_level
-1
+2
 SET @@session.optimizer_prune_level = @start_session_value;
 SELECT @@session.optimizer_prune_level;
 @@session.optimizer_prune_level
-1
+2