Support direct connections from inputs to outputs without reaction in between

[cmnrd]

In lf-lang/lingua-franca#1321, @petervdonovan pointed out that the following program fails to execute:

target Cpp

reactor ReactorWithMultiport {
    input[3] in: int

    reaction(in) {=
        for (auto i = 0; i < in.size(); i++) {
            if (in[i].is_present()) {
                std::cout << "received input at port " << i << std::endl;
            }
        }
    =}
}

reactor MultiportSplitter {
    output[3] out: int

    input in0: int
    input in1: int
    input in2: int

    in0, in1, in2 -> out
}

main reactor IndexIntoMultiportInput {
    splitter = new MultiportSplitter()
    receiver = new ReactorWithMultiport()

    splitter.out -> receiver.in

    reaction(startup) -> splitter.in1 {=
        splitter.in1.set(42);
    =}
}

The problem is located here, as there is no case for directly connecting an input to an output of the same reactor.