add APIs to determine a class is a namedtuple or PyStructSequence (#113257)

Summary:
Changes in this PR:

1. Add `is_structseq` and `is_structseq_class` functions to determine a object or a class is PyStructSequence.
2. Add a generic class `structseq` which can be used as the registration key for PyStructSequence types like `namedtuple` for Named Tuple types.
3. Change `is_namedtuple` to accept subclasses of namedtuple to be namedtuple. Before this PR, only namedtuple class directly created by `collections.namedtuple` or `typing.NamedTuple` were namedtuple classes while their subclasses were not. This PR makes `is_namedtuple` return true for subclasses of namedtuple class.

Resolves #75982. New tests are included in this PR.

- #75982

X-link: pytorch/pytorch#113257
Approved by: https://github.com/zou3519

Reviewed By: clee2000

Differential Revision: D72251158

fbshipit-source-id: cd57a40c0507ff7cb21fc42f42d42edf95379eef

Author: generatedunixname499836121

userbenchmark/dynamo/dynamobench/common.py

@@ -1397,7 +1397,7 @@ def load(cls, model, example_inputs):
                 # see https://github.com/pytorch/pytorch/issues/113029
                 example_outputs = copy.deepcopy(model)(*example_args, **example_kwargs)
 
-            if pytree._is_namedtuple_instance(example_outputs):
+            if pytree.is_namedtuple_instance(example_outputs):
                 typ = type(example_outputs)
                 pytree._register_namedtuple(
                     typ,