Add display of internal circuits for ControlFlowOps to mpl circuit drawer

[enavarro51]

Summary

This PR adds display of the circuits inside ForLoopOps and SwitchCaseOps to the mpl circuit drawer

Details and comments

This PR should be merged after #10096 and #10170. This adds the display of ForLoopOps and SwitchCaseOps in the same manner as was done in #10170 for IfElseOps and WhileLoopOps. This also fixes a bug in how gates were folding introduced in #10170.

• Add tests
• Release note

qr = QuantumRegister(4, "q")
cr = ClassicalRegister(3, "cr")
qc = QuantumCircuit(qr, cr)
qc.h(0)
with qc.for_loop((2, 4, 8, 16)) as i:
    qc.h(0)
    qc.h(1)
    qc.cx(0, 1)
    qc.rx(pi/i, 1)
    qc.measure(0, 0)
    qc.measure(1, 1)
    with qc.if_test((cr[2], 1)):
        qc.z(0)
qc.draw(style={"showindex": True})

from qiskit.circuit import QuantumCircuit, ClassicalRegister, QuantumRegister
qreg = QuantumRegister(3)
creg = ClassicalRegister(3)
qc = QuantumCircuit(qreg, creg)
qc.h([0, 1, 2])
qc.measure([0, 1, 2], [0, 1, 2])

with qc.switch(creg) as case:
    with case(0):
        qc.x(0)
    with case(1):
        qc.z(1)
        qc.z(1)
    with case(2, 3, 4, 5, 6):
        qc.y(0)
        qc.y(0)
        qc.y(0)
    with case(case.DEFAULT):
        qc.cx(0, 1)
qc.h(0)
qc.draw(style={"showindex": True})

[jakelishman]

Thanks so much for this Edwin. I've left a couple of minor comments in line, but mostly I'm judging by the test output for this, and it looks fantastic. I think it might be one of those things where we need to put it out in the wild, and see if other people find any issues with visualisation.

[enavarro51]

I added a test using textbook style in order to test the bug I found with text color.

[jakelishman]

Thanks so much for this, Edwin - I know it was a huge amount of work, both in design and actual execution, and I really appreciate it! These look fantastic, and I'm really keen to get them into the hands of our users, so we've got better ways to actually understand what's going on in a dynamic circuit.