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
bool commitBumpTransaction(const uint256& txid,
        CMutableTransaction&& mtx,
        std::vector<bilingual_str>& errors,
        uint256& bumped_txid) override
    {
        return feebumper::CommitTransaction(*m_wallet.get(), txid, std::move(mtx), errors, bumped_txid) ==
               feebumper::Result::OK;
    }
    CTransactionRef getTx(const uint256& txid) override
    {
        LOCK(m_wallet->cs_wallet);
        auto mi = m_wallet->mapWallet.find(txid);
        if (mi != m_wallet->mapWallet.end()) {
            return mi->second.tx;
        }
        return {};
    }
    WalletTx getWalletTx(const uint256& txid) override
    {
        LOCK(m_wallet->cs_wallet);
        auto mi = m_wallet->mapWallet.find(txid);
        if (mi != m_wallet->mapWallet.end()) {
            return MakeWalletTx(*m_wallet, mi->second);
        }
        return {};
    }
    std::set<WalletTx> getWalletTxs() override