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
{
    
    
    
    
    
    CFeeRate minMempoolFeeRate = wallet.chain().mempoolMinFee();
    if (newFeerate.GetFeePerK() < minMempoolFeeRate.GetFeePerK()) {
        errors.push_back(strprintf(
            Untranslated("New fee rate (%s) is lower than the minimum fee rate (%s) to get into the mempool -- "),
            FormatMoney(newFeerate.GetFeePerK()),
            FormatMoney(minMempoolFeeRate.GetFeePerK())));
        return feebumper::Result::WALLET_ERROR;
    }