Incorrect program generated when iteratively updating a variable which was initialized with a Python value

[rmshaffer]

Example which currently does not produce a correct program:

@aq.main(num_qubits=3)
def main():
    val = 0.5
    for i in aq.range(3):
        val = val + measure(i)
    return val

Either need to handle this correctly, or raise an appropriate exception with instructions on how to fix it.

This issue is extracted from amazon-braket/amazon-braket-sdk-python#929, since it was not fixed by the corresponding PR amazon-braket/amazon-braket-sdk-python#930.

A possible starting point for detecting/fixing this can be found on this branch:
amazon-braket/amazon-braket-sdk-python@feature/autoqasm...rmshaffer/autoqasm-py-value-iterative-assignment