MDEV-39585: Support SHUTDOWN command on Windows in bootstrap

Don't perform mysqld_win_initiate_shutdown under --bootstrap when
triggered by SHUTDOWN. With this we don't perform any service
interactions.

Then the shutdown can proceeded without then hard process termination
in mysqld_win_initiate_shutdown. This previously occurred because the
handle_connections_win() was never called in --bootstrap and therefore
startup_complete() was false.

Thanks Vladislav Vaintroub for investigation and providing
implementation guidance.

Author: grooverdan

sql/mysqld.cc

@@ -1667,7 +1667,8 @@ static void break_connect_loop()
   abort_loop= 1;
 
 #if defined(_WIN32)
-  mysqld_win_initiate_shutdown();
+  if (!opt_bootstrap)
+    mysqld_win_initiate_shutdown();
 #else
   mysql_mutex_lock(&LOCK_start_thread);
   if (termination_event_fd >= 0)