MDEV-29166: reduce locking of innodb rseg for user exposure of innodb_history_list_length

SHOW ENGINE INNODB STATUS and SHOW GLOBAL VARIABLES were blocking on the locks used
to access the history length in MDEV-29141. While the reason for the blockage
was elsewhere, we should make these monitoring commands less blocking as there
is a trx_sys.history_size_approx function that can be used.

SHOW ENGINE INNODB STATUS and SHOW GLOBAL STATUS LIKE
'innodb_history_list_length' and Innodb Monitors can use
trx_sys.history_size_approx().

storage/innobase/lock/lock0lock.cc

@@ -4368,7 +4368,7 @@ lock_print_info_summary(
 		? (purge_sys.running() ? "running"
 		   : purge_sys.paused() ? "stopped" : "running but idle")
 		: "disabled",
-		trx_sys.history_size());
+		trx_sys.history_size_approx());
 
 #ifdef PRINT_NUM_OF_LOCK_STRUCTS
 	fprintf(file,

storage/innobase/srv/srv0mon.cc

@@ -1682,7 +1682,7 @@ srv_mon_process_existing_counter(
 		break;
 
 	case MONITOR_RSEG_HISTORY_LEN:
-		value = trx_sys.history_size();
+		value = trx_sys.history_size_approx();
 		break;
 
 	case MONITOR_RSEG_CUR_SIZE:

storage/innobase/srv/srv0srv.cc

@@ -1085,7 +1085,7 @@ srv_export_innodb_status(void)
 		- UT_LIST_GET_LEN(buf_pool.free);
 
 	export_vars.innodb_max_trx_id = trx_sys.get_max_trx_id();
-	export_vars.innodb_history_list_length = trx_sys.history_size();
+	export_vars.innodb_history_list_length = trx_sys.history_size_approx();
 
 	export_vars.innodb_log_waits = srv_stats.log_waits;