MDEV-16372 ER_BASE64_DECODE_ERROR upon replaying binary log via mysqlbinlog --verbose

(This commit is for 10.3 and upper branches)

In case of a pattern of non-STMT_END-marked Rows-log-event (A) followed by
a STMT_END marked one (B) mysqlbinlog mixes up the base64 encoded rows events
with their pseudo sql representation produced by the verbose option:
      BINLOG '
        base64 encoded data for A
        ### verbose section for A
        base64 encoded data for B
        ### verbose section for B
      '/*!*/;
In effect the produced BINLOG '...' query is not valid and is rejected with the error.
Examples of this way malformed BINLOG could have been found in binlog_row_annotate.result
that gets corrected with the patch.

The issue is fixed with introduction an auxiliary IO_CACHE to hold on the verbose
comments until the terminal STMT_END event is found. The new cache is emptied
out after two pre-existing ones are done at that time.
The correctly produced output now for the above case is as the following:
      BINLOG '
        base64 encoded data for A
        base64 encoded data for B
      '/*!*/;
        ### verbose section for A
        ### verbose section for B

Thanks to Alexey Midenkov for the problem recognition and attempt to tackle,
and to Venkatesh Duggirala who produced a patch for the upstream whose
idea is exploited here, as well as to MDEV-23077 reporter LukeXwang who
also contributed a piece of a patch aiming at this issue.

mysql-test/suite/binlog/r/binlog_mysqlbinlog_row.result

@@ -5356,7 +5356,5 @@ START TRANSACTION
 #010909  4:46:40 server id 1  end_log_pos # CRC32 XXX 	Table_map: `test`.`t1dec102` mapped to number #
 # at #
 #010909  4:46:40 server id 1  end_log_pos # CRC32 XXX 	Write_rows: table id # flags: STMT_END_F
-### INSERT INTO `test`.`t1dec102`
-### SET
-###   @1=
+
 Error: Found Old DECIMAL (mysql-4.1 or earlier). Not enough metadata to display the value.