Turn the remaining three `binlog*` options binlog_do_db, binlog_ignore_db,
binlog_rows_event_max_size into global variables so that they can be
visible from the SQL user level. This is for audit / secure
configuration check purposes.

Create new MTR tests to make sure that the newly created global
variables can be visible from the command line interface.

Behavior before the code change:

    MariaDB [(none)]> SHOW GLOBAL VARIABLES WHERE
        -> Variable_name LIKE 'binlog_do_db' OR
        -> Variable_name LIKE 'binlog_ignore_db' OR
        -> Variable_name LIKE 'binlog_row_event_max_size';
    Empty set (0.001 sec)

Behavior after the code change:

    MariaDB [(none)]> SHOW GLOBAL VARIABLES WHERE
        -> Variable_name LIKE 'binlog_do_db' OR
        -> Variable_name LIKE 'binlog_ignore_db' OR
        -> Variable_name LIKE 'binlog_row_event_max_size';
    +---------------------------+-------+
    | Variable_name             | Value |
    +---------------------------+-------+
    | binlog_do_db              |       |
    | binlog_ignore_db          |       |
    | binlog_row_event_max_size | 8192  |
    +---------------------------+-------+
    3 rows in set (0.001 sec)

Note:

For `binlog_do_db` and `binlog_ignore_db`, we add a new class
`Sys_var_binlog_filter` to handle the dynamically-composable command line
options for `binlog_do_db` and `binlog_ignore_db`. Below
is the motivation:

When the users start the server with the option
    --binlog-do-db="database1" --binlog-do-db="database2"
The expected behavior is that the system should allow replication for
both `database1` and `database2`, which is the logic of the original
code.

However, when turning the variables into system variables, the
functionality does not exist any more, since system variables will only
handle the last occurrence of the option, and in this case, the system
will only be able to handle `database2`.

Copyright:

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.