message: Implement GetReservedDestination in DescriptorScriptPubKeyMan
diff: @@ -1603,7 +1603,11 @@ bool DescriptorScriptPubKeyMan::Encrypt(const CKeyingMaterial& master_key, Walle
  bool DescriptorScriptPubKeyMan::GetReservedDestination(const OutputType type, bool internal, CTxDestination& address, int64_t& index, CKeyPool& keypool)
  {
  - return false;
  + LOCK(cs_desc_man);
  + std::string error;
  + bool result = GetNewDestination(type, address, error);
  + index = m_wallet_descriptor.next_index - 1;
  + return result;
  }
  void DescriptorScriptPubKeyMan::ReturnDestination(int64_t index, bool internal, const CTxDestination& addr)
  