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 getMinimumFee(unsigned int tx_bytes,
        const CCoinControl& coin_control,
        int* returned_target,
        FeeReason* reason) override
    {
        FeeCalculation fee_calc;
        CAmount result;
        result = GetMinimumFee(*m_wallet, tx_bytes, coin_control, &fee_calc);
        if (returned_target) *returned_target = fee_calc.returnedTarget;
        if (reason) *reason = fee_calc.reason;
        return result;
    }
    unsigned int getConfirmTarget() override { return m_wallet->m_confirm_target; }
    bool hdEnabled() override { return m_wallet->IsHDEnabled(); }
    bool canGetAddresses() override { return m_wallet->CanGetAddresses(); }
    bool hasExternalSigner() override { return m_wallet->IsWalletFlagSet(WALLET_FLAG_EXTERNAL_SIGNER); }
    bool privateKeysDisabled() override { return m_wallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS); }
    bool taprootEnabled() override {