extmod/machine_signal: Support all Pin's arguments to the constructor.
This implements the orginal idea is that Signal is a subclass of Pin, and thus can accept all the same argument as Pin, and additionally, "inverted" param. On the practical side, it allows to avoid many enclosed parenses for a typical declararion, e.g. for Zephyr: Signal(Pin(("GPIO_0", 1))). Of course, passing a Pin to Signal constructor is still supported and is the most generic form (e.g. Unix port will only support such form, as it doesn't have "builtin" Pins), what's introduces here is just practical readability optimization. "value" kwarg is treated as applying to a Signal (i.e. accounts for possible inversion).