Introduce wrappers around CBitcoinAddress

This patch removes the need for the intermediary Base58 type
CBitcoinAddress, by providing {Encode,Decode,IsValid}Destination
function that directly operate on the conversion between strings
and CTxDestination.

src/core_write.cpp

@@ -148,8 +148,9 @@ void ScriptPubKeyToUniv(const CScript& scriptPubKey,
     out.pushKV("type", GetTxnOutputType(type));
 
     UniValue a(UniValue::VARR);
-    for (const CTxDestination& addr : addresses)
-        a.push_back(CBitcoinAddress(addr).ToString());
+    for (const CTxDestination& addr : addresses) {
+        a.push_back(EncodeDestination(addr));
+    }
     out.pushKV("addresses", a);
 }