MDEV-16664: Change the default to innodb_lock_schedule_algorithm=fcfs

The parameter innodb_lock_schedule_algorithm was introduced in
MariaDB Server 10.1.19, 10.2.13, 10.3.4 as part of MDEV-11039.
In MariaDB 10.1, the default value of the parameter is 'fcfs',
that is, the existing algorithm is used by default. But in
later versions of MariaDB Server, the parameter was 'vats',
enabling the new algorithm.

Because the new algorithm is triggering a debug assertion failure
that suggests corruption of the transactional lock data structures,
we will revert to the old algorithm by default until we have
resolved the problem.

mysql-test/suite/sys_vars/r/sysvars_innodb.result

@@ -1604,9 +1604,9 @@ READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	NONE
 VARIABLE_NAME	INNODB_LOCK_SCHEDULE_ALGORITHM
 SESSION_VALUE	NULL
-GLOBAL_VALUE	vats
+GLOBAL_VALUE	fcfs
 GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	vats
+DEFAULT_VALUE	fcfs
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	ENUM
 VARIABLE_COMMENT	The algorithm Innodb uses for deciding which locks to grant next when a lock is released. Possible values are FCFS grant the locks in First-Come-First-Served order; VATS use the Variance-Aware-Transaction-Scheduling algorithm, which uses an Eldest-Transaction-First heuristic.

storage/innobase/handler/ha_innodb.cc

@@ -20424,7 +20424,7 @@ static MYSQL_SYSVAR_ENUM(lock_schedule_algorithm, innodb_lock_schedule_algorithm
   " VATS"
   " use the Variance-Aware-Transaction-Scheduling algorithm, which"
   " uses an Eldest-Transaction-First heuristic.",
-  NULL, NULL, INNODB_LOCK_SCHEDULE_ALGORITHM_VATS,
+  NULL, NULL, INNODB_LOCK_SCHEDULE_ALGORITHM_FCFS,
   &innodb_lock_schedule_algorithm_typelib);
 
 static MYSQL_SYSVAR_ULONG(buffer_pool_instances, srv_buf_pool_instances,