Restartable poller prototype

[lmazuel]

Implement a (not tested yet) restartable poller.

The idea is that autorest changes this (the callback currently generated):

        def get_long_running_output(pipeline_response):
            response_headers = {}
            response = pipeline_response.http_response
            response_headers['Azure-AsyncOperation']=self._deserialize('str', response.headers.get('Azure-AsyncOperation'))
            response_headers['Location']=self._deserialize('str', response.headers.get('Location'))
            response_headers['Retry-After']=self._deserialize('int', response.headers.get('Retry-After'))
            deserialized = self._deserialize('Product', pipeline_response)

            if cls:
                return cls(pipeline_response, deserialized, response_headers)
            return deserialized
...
    return LROPoller(self._client, raw_result, get_long_running_output, polling_method)

to this

deserializer = MsrestDeserializer(
   self._deserialize,
   'Product',
   {'Azure-AsyncOperation':'str',
    'Location':'str',
    'Retry-After':'int'},
   cls
)
...
return LROPoller(self._client, raw_result, deserializer, polling_method)

Then it's possible to do something like:

poller = client.begin_create()
import pickle
serialized_poller = pickle.dumps(poller)
...
poller = LROPoller.from_serialized(client, serialized_poller, cls=lambda x,y,z: y)

[lmazuel]

See #10801 instead