Persist Sapling payment address to IVK map

This ensures we remember any diversified addresses manually generated
outside the wallet.

src/wallet/wallet.h

@@ -1075,6 +1075,9 @@ public:
     bool AddSaplingZKey(
         const libzcash::SaplingExtendedSpendingKey &key,
         const libzcash::SaplingPaymentAddress &defaultAddr);
+    bool AddSaplingIncomingViewingKey(
+        const libzcash::SaplingIncomingViewingKey &ivk,
+        const libzcash::SaplingPaymentAddress &addr);
     bool AddCryptedSaplingSpendingKey(
         const libzcash::SaplingExtendedFullViewingKey &extfvk,
         const std::vector<unsigned char> &vchCryptedSecret,
@@ -1083,6 +1086,11 @@ public:
     bool LoadSaplingZKey(const libzcash::SaplingExtendedSpendingKey &key);
     //! Load spending key metadata (used by LoadWallet)
     bool LoadSaplingZKeyMetadata(const libzcash::SaplingIncomingViewingKey &ivk, const CKeyMetadata &meta);
+    //! Adds a Sapling payment address -> incoming viewing key map entry,
+    //! without saving it to disk (used by LoadWallet)
+    bool LoadSaplingPaymentAddress(
+        const libzcash::SaplingPaymentAddress &addr,
+        const libzcash::SaplingIncomingViewingKey &ivk);
     //! Adds an encrypted spending key to the store, without saving it to disk (used by LoadWallet)
     bool LoadCryptedSaplingZKey(const libzcash::SaplingExtendedFullViewingKey &extfvk,
                                 const std::vector<unsigned char> &vchCryptedSecret);