support subclasses of namedtuple type (#140534)
Summary:
Allow subclassing namedtuple type. Allow assign attributes to instances of these subtypes.
X-link: https://github.com/pytorch/pytorch/pull/140534
Approved by: https://github.com/jansel
Reviewed By: izaitsevfb
Differential Revision: D66080719
fbshipit-source-id: 5a20fa5e7908234bc6eebb0ad1a7dcd727931b62
