Fix display of CCX in a Circuit

[ausbin]

A Toffoli/CCX in Q# code is currently displayed by the circuit generation code as a controlled-controlled-CNOT instead of a controlled-controlled-X.

I tried to add a test for this, but I'm not sure if I added it in the right place.

Testing

Ran cargo test and pytest (including the integration tests dependent on qir-runner and pyqir)

Also manually tested with this script:

import qsharp

qsharp.eval('''
open Microsoft.Quantum.Arrays;

operation Example() : Result[] {
    use q = Qubit[3];
    ApplyToEach(X, Most(q));
    CCNOT(q[0], q[1], q[2]);
    MResetEachZ(q)
}
''')

print(qsharp.circuit('Example()'))

which originally printed out:

q_0    ── X ──── ● ──── M ─── |0〉 ─                                                                                                                                                                               
                 │      ╘══════════
q_1    ── X ──── ● ──── M ─── |0〉 ─
                 │      ╘══════════
q_2    ──────── CX ──── M ─── |0〉 ─
                        ╘══════════

but now it prints out the following as expected:

q_0    ── X ──── ● ──── M ─── |0〉 ─
                 │      ╘══════════
q_1    ── X ──── ● ──── M ─── |0〉 ─
                 │      ╘══════════
q_2    ───────── X ──── M ─── |0〉 ─
                        ╘══════════