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
bool complete = true;
    if (sign) EnsureWalletIsUnlocked(*pwallet);
    const TransactionError err{wallet.FillPSBT(psbtx, complete, nHashType, sign, bip32derivs, nullptr, finalize)};
    if (err != TransactionError::OK) {
        throw JSONRPCTransactionError(err);
    }
    UniValue result(UniValue::VOBJ);
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    ssTx << psbtx;
    result.pushKV("psbt", EncodeBase64(ssTx.str()));
    result.pushKV("complete", complete);
    return result;
},
    };
}
RPCHelpMan walletcreatefundedpsbt()
{
    return RPCHelpMan{"walletcreatefundedpsbt",
                "\nCreates and funds a transaction in the Partially Signed Transaction format.\n"
                "Implements the Creator and Updater roles.\n"
                "All existing inputs must either have their previous output transaction be in the wallet\n"
                "or be in the UTXO set. Solving data must be provided for non-wallet inputs.\n",
                {
                    {"inputs", RPCArg::Type::ARR, RPCArg::Optional::OMITTED_NAMED_ARG, "Leave empty to add inputs automatically. See add_inputs option.",
                        {
                            {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "",
                                {
                                    {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id"},
                                    {"vout", RPCArg::Type::NUM, RPCArg::Optional::NO, "The output number"},
                                    {"sequence", RPCArg::Type::NUM, RPCArg::DefaultHint{"depends on the value of the 'locktime' and 'options.replaceable' arguments"}, "The sequence number"},