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
"\nBumps the fee of an opt-in-RBF transaction T, replacing it with a new transaction B.\n"
        + std::string(want_psbt ? "Returns a PSBT instead of creating and signing a new transaction.\n" : "") +
        "An opt-in RBF transaction with the given txid must be in the wallet.\n"
        "The command will pay the additional fee by reducing change outputs or adding inputs when necessary.\n"
        "It may add a new change output if one does not already exist.\n"
        "All inputs in the original transaction will be included in the replacement transaction.\n"
        "The command will fail if the wallet or mempool contains a transaction that spends one of T's outputs.\n"
        "By default, the new fee will be calculated automatically using the estimatesmartfee RPC.\n"
        "The user can specify a confirmation target for estimatesmartfee.\n"
        "Alternatively, the user can specify a fee rate in " + CURRENCY_ATOM + "/vB for the new transaction.\n"
        "At a minimum, the new fee rate must be high enough to pay an additional new relay fee (incrementalfee\n"
        "returned by getnetworkinfo) to enter the node's mempool.\n"
        "* WARNING: before version 0.21, fee_rate was in " + CURRENCY_UNIT + "/kvB. As of 0.21, fee_rate is in " + CURRENCY_ATOM + "/vB. *\n",
        {
            {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The txid to be bumped"},
            {"options", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED_NAMED_ARG, "",
                {
                    {"conf_target", RPCArg::Type::NUM, RPCArg::DefaultHint{"wallet -txconfirmtarget"}, "Confirmation target in blocks\n"},
                    {"fee_rate", RPCArg::Type::AMOUNT, RPCArg::DefaultHint{"not set, fall back to wallet fee estimation"},
                             "\nSpecify a fee rate in " + CURRENCY_ATOM + "/vB instead of relying on the built-in fee estimator.\n"
                             "Must be at least " + incremental_fee + " higher than the current transaction fee rate.\n"
                             "WARNING: before version 0.21, fee_rate was in " + CURRENCY_UNIT + "/kvB. As of 0.21, fee_rate is in " + CURRENCY_ATOM + "/vB.\n"},
                    {"replaceable", RPCArg::Type::BOOL, RPCArg::Default{true}, "Whether the new transaction should still be\n"
                             "marked bip-125 replaceable. If true, the sequence numbers in the transaction will\n"
                             "be left unchanged from the original. If false, any input sequence numbers in the\n"
                             "original transaction that were less than 0xfffffffe will be increased to 0xfffffffe\n"
                             "so the new transaction will not be explicitly bip-125 replaceable (though it may\n"
                             "still be replaceable in practice, for example if it has unconfirmed ancestors which\n"
                             "are replaceable).\n"},
                    {"estimate_mode", RPCArg::Type::STR, RPCArg::Default{"unset"}, "The fee estimate mode, must be one of (case insensitive):\n"