Add skeleton chain and client classes

This commit does not change behavior. It just adds new skeleton classes that
don't do anything and aren't instantiated yet.

src/interfaces/wallet.cpp

@@ -7,6 +7,7 @@
 #include <amount.h>
 #include <chain.h>
 #include <consensus/validation.h>
+#include <interfaces/chain.h>
 #include <interfaces/handler.h>
 #include <net.h>
 #include <policy/feerate.h>
@@ -20,11 +21,17 @@
 #include <timedata.h>
 #include <ui_interface.h>
 #include <uint256.h>
+#include <util/system.h>
 #include <validation.h>
 #include <wallet/feebumper.h>
 #include <wallet/fees.h>
 #include <wallet/wallet.h>
 
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
 namespace interfaces {
 namespace {
 
@@ -456,8 +463,25 @@ public:
     CWallet& m_wallet;
 };
 
+class WalletClientImpl : public ChainClient
+{
+public:
+    WalletClientImpl(Chain& chain, std::vector<std::string> wallet_filenames)
+        : m_chain(chain), m_wallet_filenames(std::move(wallet_filenames))
+    {
+    }
+
+    Chain& m_chain;
+    std::vector<std::string> m_wallet_filenames;
+};
+
 } // namespace
 
 std::unique_ptr<Wallet> MakeWallet(const std::shared_ptr<CWallet>& wallet) { return MakeUnique<WalletImpl>(wallet); }
 
+std::unique_ptr<ChainClient> MakeWalletClient(Chain& chain, std::vector<std::string> wallet_filenames)
+{
+    return MakeUnique<WalletClientImpl>(chain, std::move(wallet_filenames));
+}
+
 } // namespace interfaces