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
{
    CKeyID keyid = pubkey.GetID();
    const auto it = sigdata.signatures.find(keyid);
    if (it != sigdata.signatures.end()) {
        sig_out = it->second.second;
        return true;
    }
    KeyOriginInfo info;
    if (provider.GetKeyOrigin(keyid, info)) {
        sigdata.misc_pubkeys.emplace(keyid, std::make_pair(pubkey, std::move(info)));
    }
    if (creator.CreateSig(provider, sig_out, keyid, scriptcode, sigversion)) {
        auto i = sigdata.signatures.emplace(keyid, SigPair(pubkey, sig_out));
        assert(i.second);
        return true;
    }
    
    sigdata.missing_sigs.push_back(keyid);
    return false;
}
static bool CreateTaprootScriptSig(const BaseSignatureCreator& creator, SignatureData& sigdata, const SigningProvider& provider, std::vector<unsigned char>& sig_out, const XOnlyPubKey& pubkey, const uint256& leaf_hash, SigVersion sigversion)