Add __set_name__

[gingershaped]

CircuitPython lacks support for object.__set_name__, a dunder method added in 3.6 which allows descriptors to know the name they were assigned to in their owning class. This makes descriptor implementations have needless redundancy:

class FooDescriptor:
    def __init__(self, name):
        self.name = name
    # def __set_name__(self, owner, name):
    #    self.name = name
class Foo:
    thing = FooDescriptor("thing")

My use-case for this is a utility descriptor which wraps a property of its owning class and invokes an updater method when it's set:

class HardwareState:
    class Property:
        def __init__(self, name, initial_value):
            self.name = "_" + name
            self.initial_value = initial_value
        def __get__(self, instance: Hardware, owner):
            if not hasattr(instance, self.name):
                self.__set__(instance, self.initial_value)
            return getattr(instance, self.name)
        def __set__(self, instance: Hardware, value):
            setattr(instance, self.name, value)
            if instance.active:
                instance.apply()
    
    ring_color = Property("ring_color", 0x000000)
    ring_brightness = Property("ring_brightness", 1)
    status_color = Property("status_color", 0x000000)
    status_brightness = Property("status_brightness", 1)
    speaker_muted = Property("speaker_muted", True)
    # ...

[dhalbert]

There is work going on upstream in MicroPython to add __set_name__. When this is merged into MicroPython, we'll merge it into CircuitPython in one of our periodic merges from upstream.
micropython#15501
micropython#15503