rpc: deprecate addresses and reqSigs from rpc outputs

1) add a new sane "address" field (for outputs that have an
   identifiable address, which doesn't include bare multisig)
2) with -deprecatedrpc: leave "reqSigs" and "addresses" intact
   (with all weird/wrong behavior they have now)
3) without -deprecatedrpc: drop "reqSigs" and "addresses" entirely,
   always.

src/script/standard.cpp

@@ -220,7 +220,6 @@ bool ExtractDestination(const CScript& scriptPubKey, CTxDestination& addressRet)
         return true;
     }
     case TxoutType::MULTISIG:
-        // Multisig txns have more than one address...
     case TxoutType::NULL_DATA:
     case TxoutType::NONSTANDARD:
         return false;
@@ -228,6 +227,7 @@ bool ExtractDestination(const CScript& scriptPubKey, CTxDestination& addressRet)
     assert(false);
 }
 
+// TODO: from v23 ("addresses" and "reqSigs" deprecated) "ExtractDestinations" should be removed
 bool ExtractDestinations(const CScript& scriptPubKey, TxoutType& typeRet, std::vector<CTxDestination>& addressRet, int& nRequiredRet)
 {
     addressRet.clear();

src/script/standard.h

@@ -247,6 +247,8 @@ bool ExtractDestination(const CScript& scriptPubKey, CTxDestination& addressRet)
  * Note: this function confuses destinations (a subset of CScripts that are
  * encodable as an address) with key identifiers (of keys involved in a
  * CScript), and its use should be phased out.
+ *
+ * TODO: from v23 ("addresses" and "reqSigs" deprecated) "ExtractDestinations" should be removed
  */
 bool ExtractDestinations(const CScript& scriptPubKey, TxoutType& typeRet, std::vector<CTxDestination>& addressRet, int& nRequiredRet);