Avoid triggering reportUnreachable on exception raising?

(Acknowledging that this is a new and disabled-by-default rule)

Currently pyright will trigger reportUnreachable on the following code:

def foo(x: int | str):
    if isinstance(x, int):
        print("int")
    elif isinstance(x, str):
        print("str")
    else:
        raise ValueError  # error

mypy's version of the same rule ignores unreachable statements that are of a small set of forms, like raise (expr) or assert False, or statements are equivalent to a correctly used assert_never: https://github.com/python/mypy/blob/master/mypy/checker.py#L3139-L3165

This makes these diagnostics substantially higher signal

Start with pyright's reportUnreachable handling and compare it with the linked mypy checker.py logic for ignored unreachable forms. Use the provided isinstance example to verify that the raise statement no longer produces a diagnostic while other unreachable statements still do.