MDEV-22683: Ensure system tables are correctly upgraded in MariaDB 10.4

Running mysql_upgrade should end up with the exact same system tables as fresh
installations have after running mysql_install_db. To ensure the upgrade is
correct and complete:

- Remove the redundant modification of thread_id`. On 5.5 version, the
  `general_log` table was created as `CREATE TABLE IF NOT EXISTS general_log
  (..., thread_id INTEGER NOT NULL, ...)`, and starting from 10.0+, the table is
  created as `CREATE TABLE IF NOT EXISTS general_log (..., thread_id BIGINT(21)
  UNSIGNED NOT NULL, ...)`, but mysql_upgrade is not properly upgrading the
  table. It modifies the `thread_id` twice in one query, which could leave the
  table not modified and lead to other potential error when upgrading from
  MariaDB 5.5 or older.

- Update `servers` to ensure `Host` and `User` has correct data type if
  upgrading from 10.1 or older. On versions 10.0 and 10.1, the `servers` table
  was created as `CREATE TABLE IF NOT EXISTS servers (..., Host char(64) NOT
  NULL DEFAULT , ..., Owner char(64) NOT NULL DEFAULT , ...)`, and starting
  from 10.2, the table is created as `CREATE TABLE IF NOT EXISTS servers (...,
  Host varchar(2048) NOT NULL DEFAULT , ..., Owner varchar(512) NOT NULL
  DEFAULT , ...)`.

All new code of the whole pull request, including one or several files that
are either new files or modified ones, are contributed under the BSD-new license.
I am contributing on behalf of my employer Amazon Web Services, Inc.

mysql-test/main/system_mysql_db_fix50030.result

@@ -166,14 +166,14 @@ show create table servers;
 Table	Create Table
 servers	CREATE TABLE `servers` (
   `Server_name` char(64) NOT NULL DEFAULT '',
-  `Host` char(64) NOT NULL DEFAULT '',
+  `Host` varchar(2048) NOT NULL DEFAULT '',
   `Db` char(64) NOT NULL DEFAULT '',
   `Username` char(80) NOT NULL DEFAULT '',
   `Password` char(64) NOT NULL DEFAULT '',
   `Port` int(4) NOT NULL DEFAULT 0,
   `Socket` char(64) NOT NULL DEFAULT '',
   `Wrapper` char(64) NOT NULL DEFAULT '',
-  `Owner` char(64) NOT NULL DEFAULT '',
+  `Owner` varchar(512) NOT NULL DEFAULT '',
   PRIMARY KEY (`Server_name`)
 ) ENGINE=Aria DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci PAGE_CHECKSUM=1 TRANSACTIONAL=1 COMMENT='MySQL Foreign Servers table'
 show create table proc;

mysql-test/main/system_mysql_db_fix50117.result

@@ -146,14 +146,14 @@ show create table servers;
 Table	Create Table
 servers	CREATE TABLE `servers` (
   `Server_name` char(64) NOT NULL DEFAULT '',
-  `Host` char(64) NOT NULL DEFAULT '',
+  `Host` varchar(2048) NOT NULL DEFAULT '',
   `Db` char(64) NOT NULL DEFAULT '',
   `Username` char(80) NOT NULL DEFAULT '',
   `Password` char(64) NOT NULL DEFAULT '',
   `Port` int(4) NOT NULL DEFAULT 0,
   `Socket` char(64) NOT NULL DEFAULT '',
   `Wrapper` char(64) NOT NULL DEFAULT '',
-  `Owner` char(64) NOT NULL DEFAULT '',
+  `Owner` varchar(512) NOT NULL DEFAULT '',
   PRIMARY KEY (`Server_name`)
 ) ENGINE=Aria DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci PAGE_CHECKSUM=1 TRANSACTIONAL=1 COMMENT='MySQL Foreign Servers table'
 show create table proc;

scripts/mysql_system_tables_fix.sql

@@ -239,7 +239,6 @@ SET GLOBAL general_log = 'OFF';
 ALTER TABLE general_log
   MODIFY event_time TIMESTAMP(6) NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
   MODIFY user_host MEDIUMTEXT NOT NULL,
-  MODIFY thread_id INTEGER NOT NULL,
   MODIFY server_id INTEGER UNSIGNED NOT NULL,
   MODIFY command_type VARCHAR(64) NOT NULL,
   MODIFY argument MEDIUMTEXT NOT NULL,
@@ -841,3 +840,8 @@ IF 1 = (SELECT count(*) FROM information_schema.VIEWS WHERE TABLE_CATALOG = 'def
 END IF//
 
 DELIMITER ;
+
+# MDEV-22683 - upgrade Host and Owner of servers
+ALTER TABLE servers
+  MODIFY Host varchar(2048) NOT NULL DEFAULT '',
+  MODIFY Owner varchar(512) NOT NULL DEFAULT '';