MDEV-13564: Set innodb_safe_truncate=ON by default

The setting innodb_safe_truncate=ON reduces compatibility with older
versions of MariaDB and backup tools in two ways.

First, we will be writing TRX_UNDO_RENAME_TABLE records, which older
versions do not know about. These records could be misinterpreted if
a DDL transaction was recovered and would be rolled back.
Such rollback is only possible if the server was killed while
an incomplete DDL transaction was persisted. On transaction completion,
the insert_undo log pages would only be repurposed for new undo log
allocations, and their contents would not matter. So, older versions
will not have a problem with innodb_safe_truncate=ON if the server was
shut down cleanly.

Second, to prevent such recovery failure, innodb_safe_truncate=ON will
cause a modification of the redo log format identifier, which will
prevent older versions from starting up after a crash. MariaDB Server
versions older than 10.2.13 will refuse to start up altogether, even
after clean shutdown.

A server restart with innodb_safe_truncate=OFF will restore compatibility
with older server and backup versions.

mysql-test/suite/innodb/t/truncate_debug.opt

+--innodb-safe-truncate=0

mysql-test/suite/innodb/t/truncate_inject.opt

+--innodb-safe-truncate=0

mysql-test/suite/innodb/t/truncate_purge_debug.opt

 --innodb-purge-threads=1
 --innodb-purge-batch-size=1
 --innodb-stats-persistent=OFF
+--innodb-safe-truncate=0

mysql-test/suite/innodb/t/truncate_restart.opt

+--innodb-safe-truncate=0

mysql-test/suite/innodb_zip/t/wl6501_1.opt

+--innodb-safe-truncate=0

mysql-test/suite/innodb_zip/t/wl6501_crash_3.opt

+--innodb-safe-truncate=0

mysql-test/suite/innodb_zip/t/wl6501_crash_4.opt

+--innodb-safe-truncate=0

mysql-test/suite/innodb_zip/t/wl6501_crash_5.opt

+--innodb-safe-truncate=0

mysql-test/suite/innodb_zip/t/wl6501_scale_1.opt

+--innodb-safe-truncate=0

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

@@ -2402,12 +2402,12 @@ READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	OPTIONAL
 VARIABLE_NAME	INNODB_SAFE_TRUNCATE
 SESSION_VALUE	NULL
-GLOBAL_VALUE	OFF
+GLOBAL_VALUE	ON
 GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	OFF
+DEFAULT_VALUE	ON
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	BOOLEAN
-VARIABLE_COMMENT	Use backup-safe TRUNCATE TABLE and crash-safe RENAME (incompatible with older MariaDB 10.2; OFF by default)
+VARIABLE_COMMENT	Use backup-safe TRUNCATE TABLE and crash-safe RENAME (incompatible with older MariaDB 10.2; ON by default)
 NUMERIC_MIN_VALUE	NULL
 NUMERIC_MAX_VALUE	NULL
 NUMERIC_BLOCK_SIZE	NULL

storage/innobase/handler/ha_innodb.cc

@@ -20696,8 +20696,8 @@ static MYSQL_SYSVAR_BOOL(read_only, srv_read_only_mode,
 
 static MYSQL_SYSVAR_BOOL(safe_truncate, srv_safe_truncate,
   PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_READONLY,
-  "Use backup-safe TRUNCATE TABLE and crash-safe RENAME (incompatible with older MariaDB 10.2; OFF by default)",
-  NULL, NULL, FALSE);
+  "Use backup-safe TRUNCATE TABLE and crash-safe RENAME (incompatible with older MariaDB 10.2; ON by default)",
+  NULL, NULL, TRUE);
 
 static MYSQL_SYSVAR_BOOL(cmp_per_index_enabled, srv_cmp_per_index_enabled,
   PLUGIN_VAR_OPCMDARG,