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
CAmount new_total_fee = newFeerate.GetFee(maxTxSize);
    CFeeRate incrementalRelayFee = std::max(wallet.chain().relayIncrementalFee(), CFeeRate(WALLET_INCREMENTAL_RELAY_FEE));
    
    isminefilter filter = wallet.GetLegacyScriptPubKeyMan() && wallet.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS) ? ISMINE_WATCH_ONLY : ISMINE_SPENDABLE;
    CAmount old_fee = CachedTxGetDebit(wallet, wtx, filter) - wtx.tx->GetValueOut();
    const int64_t txSize = GetVirtualTransactionSize(*(wtx.tx));
    CFeeRate nOldFeeRate(old_fee, txSize);
    
    CAmount minTotalFee = nOldFeeRate.GetFee(maxTxSize) + incrementalRelayFee.GetFee(maxTxSize);
    if (new_total_fee < minTotalFee) {
        errors.push_back(strprintf(Untranslated("Insufficient total fee %s, must be at least %s (oldFee %s + incrementalFee %s)"),
            FormatMoney(new_total_fee), FormatMoney(minTotalFee), FormatMoney(nOldFeeRate.GetFee(maxTxSize)), FormatMoney(incrementalRelayFee.GetFee(maxTxSize))));
        return feebumper::Result::INVALID_PARAMETER;
    }
    CAmount requiredFee = GetRequiredFee(wallet, maxTxSize);
    if (new_total_fee < requiredFee) {
        errors.push_back(strprintf(Untranslated("Insufficient total fee (cannot be less than required fee %s)"),
            FormatMoney(requiredFee)));
        return feebumper::Result::INVALID_PARAMETER;
    }
    
    const CAmount max_tx_fee = wallet.m_default_max_tx_fee;
    if (new_total_fee > max_tx_fee) {
        errors.push_back(strprintf(Untranslated("Specified or calculated fee %s is too high (cannot be higher than -maxtxfee %s)"),
            FormatMoney(new_total_fee), FormatMoney(max_tx_fee)));
        return feebumper::Result::WALLET_ERROR;
    }
    return feebumper::Result::OK;
}
static CFeeRate EstimateFeeRate(const CWallet& wallet, const CWalletTx& wtx, const CAmount old_fee, const CCoinControl& coin_control)