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
WalletTxStatus& tx_status,
        WalletOrderForm& order_form,
        bool& in_mempool,
        int& num_blocks) override
    {
        LOCK(m_wallet->cs_wallet);
        auto mi = m_wallet->mapWallet.find(txid);
        if (mi != m_wallet->mapWallet.end()) {
            num_blocks = m_wallet->GetLastBlockHeight();
            in_mempool = mi->second.InMempool();
            order_form = mi->second.vOrderForm;
            tx_status = MakeWalletTxStatus(*m_wallet, mi->second);
            return MakeWalletTx(*m_wallet, mi->second);
        }
        return {};
    }
    TransactionError fillPSBT(int sighash_type,
        bool sign,
        bool bip32derivs,
        size_t* n_signed,
        PartiallySignedTransaction& psbtx,
        bool& complete) override
    {
        return m_wallet->FillPSBT(psbtx, complete, sighash_type, sign, bip32derivs, n_signed);
    }
    WalletBalances getBalances() override