WL#7083 step 6.4. GTID-violations: User-visible changes for counters of GTID-violating transactions.

This patch introduces the following user-visible changes related to the
counters that keep track of the number of ongoing GTID-violating
transactions:

- Generate error when user tries to change from GTID_MODE=OFF_PERMISSIVE
to ON_PERMISSIVE, when there are ongoing GTID-violating transactions
using GTID_NEXT=AUTOMATIC.

- Generate error when user tries to change from
ENFORCE_GTID_CONSISTENCY=WARN or OFF to ON, if there are ongoing GTID-
violating transactions.

- Generate error when user tries to change from
ENFORCE_GTID_CONSISTENCY=OFF to WARN, if there are ongoing GTID-
violating transactions.

- When debug mode is enabled, the counters are visible as the status
variables AUTOMATIC_GTID_VIOLATING_TRANSACTION_COUNT and
ANONYMOUS_GTID_VIOLATING_TRANSACTION_COUNT.

@mysqld.cc
- Two new status variables.

@errmsg-utf8.txt
- Two new error messages.

@sys_vars.h
- Three new error conditions.