Auto merge of #3228 - str4d:3058-taddr-encoding-refactor, r=str4d

Refactor t-address encoding

Includes code cherry-picked from the following upstream PRs:

- bitcoin/bitcoin#11117
- bitcoin/bitcoin#11259
  - Only the second commit (first is for QT code)
- bitcoin/bitcoin#11167
  - Only the first commit (the rest are not part of the t-address encoding refactor).

Part of #3058. Precursor to #3202.

src/wallet/asyncrpcoperation_mergetoaddress.cpp

@@ -73,8 +73,8 @@ AsyncRPCOperation_mergetoaddress::AsyncRPCOperation_mergetoaddress(
         throw JSONRPCError(RPC_INVALID_PARAMETER, "Recipient parameter missing");
     }
 
-    toTaddr_ = CBitcoinAddress(std::get<0>(recipient));
-    isToTaddr_ = toTaddr_.IsValid();
+    toTaddr_ = DecodeDestination(std::get<0>(recipient));
+    isToTaddr_ = IsValidDestination(toTaddr_);
     isToZaddr_ = false;
 
     if (!isToTaddr_) {
@@ -246,7 +246,7 @@ bool AsyncRPCOperation_mergetoaddress::main_impl()
         rawTx.vin.push_back(in);
     }
     if (isToTaddr_) {
-        CScript scriptPubKey = GetScriptForDestination(toTaddr_.Get());
+        CScript scriptPubKey = GetScriptForDestination(toTaddr_);
         CTxOut out(sendAmount, scriptPubKey);
         rawTx.vout.push_back(out);
     }