Pass victim context for provider on BF abort

This change is needed for custom provider implementations to
have a way to access the victim in the application context.

Helper interface operation_context to pass caller context for
service/provider callbacks in more type safe way.

include/wsrep/operation_context.hpp

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2022 Codership Oy <info@codership.com>
+ *
+ * This file is part of wsrep-lib.
+ *
+ * Wsrep-lib is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * Wsrep-lib is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with wsrep-lib.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** @file operation_context.hpp
+ *
+ * A slightly more type safe way compared to void pointers to
+ * pass operation contexts through wsrep-lib to callbacks.
+ */
+
+#ifndef WSREP_OPERATION_CONTEXT_HPP
+#define WSREP_OPERATION_CONTEXT_HPP
+
+namespace wsrep
+{
+    struct operation_context
+    {
+        virtual ~operation_context() = default;
+    };
+
+    struct null_operation_context : operation_context
+    {
+    };
+} // namespace wsrep
+
+#endif /* WSREP_OPERATION_CONTEXT_HPP */