TransactionBuilder: Add change output to transaction

src/transaction_builder.h

@@ -64,6 +64,9 @@ private:
     std::vector<OutputDescriptionInfo> outputs;
     std::vector<TransparentInputInfo> tIns;
 
+    boost::optional<std::pair<libzcash::SaplingFullViewingKey, libzcash::SaplingPaymentAddress>> zChangeAddr;
+    boost::optional<CTxDestination> tChangeAddr;
+
 public:
     TransactionBuilder(const Consensus::Params& consensusParams, int nHeight, CKeyStore* keyStore = nullptr);
 
@@ -86,6 +89,10 @@ public:
 
     bool AddTransparentOutput(CTxDestination& to, CAmount value);
 
+    void SendChangeTo(libzcash::SaplingPaymentAddress changeAddr, libzcash::SaplingFullViewingKey fvkOut);
+
+    bool SendChangeTo(CTxDestination& changeAddr);
+
     boost::optional<CTransaction> Build();
 };