multiprocess: Add Ipc and Init interface definitions

src/interfaces/init.cpp

@@ -0,0 +1,15 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <interfaces/chain.h>
+#include <interfaces/init.h>
+#include <interfaces/node.h>
+#include <interfaces/wallet.h>
+
+namespace interfaces {
+std::unique_ptr<Node> Init::makeNode() { return {}; }
+std::unique_ptr<Chain> Init::makeChain() { return {}; }
+std::unique_ptr<WalletClient> Init::makeWalletClient(Chain& chain) { return {}; }
+Ipc* Init::ipc() { return nullptr; }
+} // namespace interfaces