In preparation for the potential Taproot soft fork, libconsensus should be updated to support verifying Taproot scripts.

There are two changes I see as necessary:

- Add a VERIFY_TAPROOT flag
- Change the API to support passing in spent outputs (bitcoinconsensus_verify_script_with_spent_outputs?)
{
        key0.Set(vchKey0, vchKey0 + 32, false);
        key0C.Set(vchKey0, vchKey0 + 32, true);
        pubkey0 = key0.GetPubKey();
        pubkey0H = key0.GetPubKey();
        pubkey0C = key0C.GetPubKey();
        *const_cast<unsigned char*>(pubkey0H.data()) = 0x06 | (pubkey0H[64] & 1);
        key1.Set(vchKey1, vchKey1 + 32, false);
        key1C.Set(vchKey1, vchKey1 + 32, true);
        pubkey1 = key1.GetPubKey();
        pubkey1C = key1C.GetPubKey();
        key2.Set(vchKey2, vchKey2 + 32, false);
        key2C.Set(vchKey2, vchKey2 + 32, true);
        pubkey2 = key2.GetPubKey();
        pubkey2C = key2C.GetPubKey();
    }
};
enum class WitnessMode {