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
{
        const auto bal = GetBalance(*m_wallet);
        WalletBalances result;
        result.balance = bal.m_mine_trusted;
        result.unconfirmed_balance = bal.m_mine_untrusted_pending;
        result.immature_balance = bal.m_mine_immature;
        result.have_watch_only = haveWatchOnly();
        if (result.have_watch_only) {
            result.watch_only_balance = bal.m_watchonly_trusted;
            result.unconfirmed_watch_only_balance = bal.m_watchonly_untrusted_pending;
            result.immature_watch_only_balance = bal.m_watchonly_immature;
        }
        return result;
    }
    bool tryGetBalances(WalletBalances& balances, uint256& block_hash) override
    {
        TRY_LOCK(m_wallet->cs_wallet, locked_wallet);
        if (!locked_wallet) {
            return false;
        }
        block_hash = m_wallet->GetLastBlockHash();
        balances = getBalances();
        return true;
    }
    CAmount getBalance() override { return GetBalance(*m_wallet).m_mine_trusted; }