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 getAvailableBalance(const CCoinControl& coin_control) override
    {
        return GetAvailableBalance(*m_wallet, &coin_control);
    }
    isminetype txinIsMine(const CTxIn& txin) override
    {
        LOCK(m_wallet->cs_wallet);
        return InputIsMine(*m_wallet, txin);
    }
    isminetype txoutIsMine(const CTxOut& txout) override
    {
        LOCK(m_wallet->cs_wallet);
        return m_wallet->IsMine(txout);
    }
    CAmount getDebit(const CTxIn& txin, isminefilter filter) override
    {
        LOCK(m_wallet->cs_wallet);
        return m_wallet->GetDebit(txin, filter);
    }
    CAmount getCredit(const CTxOut& txout, isminefilter filter) override
    {
        LOCK(m_wallet->cs_wallet);
        return OutputGetCredit(*m_wallet, txout, filter);
    }
    CoinsList listCoins() override