MDEV-27736 Allow seamless upgrade despite ROW_FORMAT=COMPRESSED

In commit 9bc874a (MDEV-23497)
the configuration option innodb_read_only_compressed was introduced
to giver users advance notice of a plan to remove ROW_FORMAT=COMPRESSED
support for InnoDB.

Based on user feedback, this plan has been scrapped.
Even though ROW_FORMAT=COMPRESSED is a dead end and causes some
overhead for InnoDB data structures, we can live with that.

Now that we know that some users really want to keep using
ROW_FORMAT=COMPRESSED, the previous default value of the parameter
innodb_read_only_compressed=ON should be changed to OFF, to allow
smooth upgrades to 10.6 and later versions, without requiring users
to update any configuration file.

Author: dr-m

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

@@ -1427,10 +1427,10 @@ READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	OPTIONAL
 VARIABLE_NAME	INNODB_READ_ONLY_COMPRESSED
 SESSION_VALUE	NULL
-DEFAULT_VALUE	ON
+DEFAULT_VALUE	OFF
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	BOOLEAN
-VARIABLE_COMMENT	Make ROW_FORMAT=COMPRESSED tables read-only (ON by default)
+VARIABLE_COMMENT	Make ROW_FORMAT=COMPRESSED tables read-only
 NUMERIC_MIN_VALUE	NULL
 NUMERIC_MAX_VALUE	NULL
 NUMERIC_BLOCK_SIZE	NULL

storage/innobase/handler/ha_innodb.cc

@@ -19615,8 +19615,8 @@ static MYSQL_SYSVAR_BOOL(read_only, srv_read_only_mode,
 
 static MYSQL_SYSVAR_BOOL(read_only_compressed, innodb_read_only_compressed,
   PLUGIN_VAR_OPCMDARG,
-  "Make ROW_FORMAT=COMPRESSED tables read-only (ON by default)",
-  NULL, NULL, TRUE);
+  "Make ROW_FORMAT=COMPRESSED tables read-only",
+  NULL, NULL, FALSE);
 
 static MYSQL_SYSVAR_BOOL(cmp_per_index_enabled, srv_cmp_per_index_enabled,
   PLUGIN_VAR_OPCMDARG,