Pass **kwds in MetaHasDescriptors __new__ and __init__

[fleming79]

This is a modest change that adds **kwds to MetaHasDescriptors __new__ and __init__ to match the signature defined in the Python docs:

metaclass(name, bases, namespace, **kwds)

This enables the usage __init_subclass__ without having to overload MetaHasDescriptors to intercept the arguments passed to a subclass.

Trivial example

from traitlets import HasTraits
class Philosopher(HasTraits):
    def __init_subclass__(cls, /, default_name, **kwargs):
        super().__init_subclass__(**kwargs)
        cls.default_name = default_name

class AustralianPhilosopher(Philosopher, default_name="Bruce"):
    pass

Before

After

[blink1073]

Sounds reasonable to me, thank you!