MDEV-20574 Position of events reported by mysqlbinlog is wrong with encrypted binlogs, SHOW BINLOG EVENTS reports the correct one.

Analysis

Mysqlbinlog output for encrypted binary log
#Q> insert into tab1 values (3,'row 003')
#190912 17:36:35 server id 10221  end_log_pos 980 CRC32 0x53bcb3d3  Table_map: `test`.`tab1` mapped to number 19
# at 940
#190912 17:36:35 server id 10221  end_log_pos 1026 CRC32 0xf2ae5136     Write_rows: table id 19 flags: STMT_END_F

Here we can see Table_map_log_event ends at 980 but Next event starts at 940.
And the reason for that is we do not send START_ENCRYPTION_EVENT to the slave

Solution:-
Send Start_encryption_log_event as Ignorable_log_event to slave(mysqlbinlog),
So that mysqlbinlog can update its log_pos.
Since Slave can request multiple FORMAT_DESCRIPTION_EVENT while master does not
have so We only update slave master pos when master actually have the
FORMAT_DESCRIPTION_EVENT. Similar logic should be applied for START_ENCRYPTION_EVENT.

Also added the test case when new server reads the data from old server which
does not send START_ENCRYPTION_EVENT to slave.

Master Slave Upgrade Scenario.
When Slave is updated first, Slave will have extra logic of handling
START_ENCRYPTION_EVENT But master willnot be sending START_ENCRYPTION_EVENT.
So there will be no issue.
When Master is updated first, It will send  START_ENCRYPTION_EVENT to
slave , But slave will ignore this event in queue_event.

mysql-test/suite/binlog_encryption/mysqlbinlog.test

@@ -17,5 +17,8 @@ let outfile=$MYSQLTEST_VARDIR/tmp/binlog_enc.sql;
 exec $MYSQL_BINLOG $local > $outfile;
 exec $MYSQL_BINLOG $local --force-read >> $outfile;
 exec $MYSQL_BINLOG $remote >> $outfile;
+--let SEARCH_FILE= $outfile
+--let SEARCH_PATTERN= Ignorable event type 164.*
+--source include/search_pattern_in_file.inc
 remove_file $outfile;