MDEV-31448: Killing a replica thread awaiting its GCO can hang/crash a parallel replica

Various test cases for the bugs around MDEV-31448.
Test cases due to Brandon Nesterenko, thanks!

Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

mysql-test/suite/rpl/t/rpl_parallel_kill.test

@@ -0,0 +1,15 @@
+--source include/master-slave.inc
+--source include/have_innodb.inc
+--source include/have_debug.inc
+--source include/have_binlog_format_row.inc
+
+--source include/mdev-31448_conservative.inc
+
+--let $killed_trx_commits=1
+--source include/mdev-31448_optimistic.inc
+--let $killed_trx_commits=0
+--source include/mdev-31448_optimistic.inc
+
+
+
+--source include/rpl_end.inc