Fix crash close_orphaned_sr_transactions() BF abort

Some implementations of provider `bf_abort()` require `victim_ctx`
to point to application side victim context. However, when
total order BF abort was done from `close_orphaned_sr_transactions()`,
the application side context was not available.

To fix this, added an interface method `call_in_operation_context()`
which allows invoking a function object with a reference to
application side operation context passed in as a parameter.
This method is used in `close_orphaned_sr_transactions()`
to call `client_state::total_order_bf_abort()` with appropriate
victim operation context.

dbsim/db_client_service.hpp

@@ -92,6 +92,14 @@ namespace db
             return false;
         }
 
+        void call_in_operation_context(
+            const std::function<void(wsrep::operation_context&)>& fn)
+            const override
+        {
+            wsrep::null_operation_context op;
+            fn(op);
+        }
+
         void debug_sync(const char*) override { }
         void debug_crash(const char*) override { }
     private: