Expose functionality of check_slave_start_position

The following c file...

https://github.com/MariaDB/server/blob/d4e3aa4c6f4fb467b7f1adacd8ea9f71339cffe0/sql/sql_repl.cc

Contains a function called check_slave_start_position. It would be useful to expose this, perhaps as a SQL function, in order to see if failover will function, at least from a GTID perspective.

i.e.

SELECT CHECK_SLAVE_START_POS('1-1-55');

1. Returns true if binlog contains gtid, otherwise false