External inputs are currently only supported for initial transaction creation functions. Extend `solving_data` arguments as necessary to support fee bumping wallet transactions with non-wallet inputs.

https://github.com/bitcoin/bitcoin/pull/17211#issuecomment-897653994
{
    std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(request);
    if (!pwallet) return UniValue::VNULL;
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    LOCK(pwallet->cs_wallet);
    if (!request.params[0].isNull() && !request.params[0].get_str().empty()) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Dummy value must be set to \"\"");
    }
    UniValue sendTo = request.params[1].get_obj();
    mapValue_t mapValue;
    if (!request.params[3].isNull() && !request.params[3].get_str().empty())
        mapValue["comment"] = request.params[3].get_str();
    UniValue subtractFeeFromAmount(UniValue::VARR);
    if (!request.params[4].isNull())
        subtractFeeFromAmount = request.params[4].get_array();
    CCoinControl coin_control;
    if (!request.params[5].isNull()) {
        coin_control.m_signal_bip125_rbf = request.params[5].get_bool();
    }
    SetFeeEstimateMode(*pwallet, coin_control, request.params[6], request.params[7], request.params[8], false);
    std::vector<CRecipient> recipients;
    ParseRecipients(sendTo, subtractFeeFromAmount, recipients);
    const bool verbose{request.params[9].isNull() ? false : request.params[9].get_bool()};
    return SendMoney(*pwallet, coin_control, recipients, std::move(mapValue), verbose);
},
    };
}
RPCHelpMan settxfee()