CDK: Add support for streams with state attribute (state v2)

[keu]

Tell us about the problem you're trying to solve

Facebook Marketing is a good example of why the state should be an explicit attribute of the stream.
An incremental stream is a cursor slicing through the remote data, it is wrong to assume that the state (cursor position) depends only on the latest record that we read. Therefore we should use explicit state get and set constructions (the version that we used in base python before introducing CDK). This will allow setting the state explicitly before any reading operation (stream_slices depends on state value because we save state for each slice individually in FB Marketing).

Another example:
Let's say we have reversed incremental stream, that stream updates its state only once - at the end of the reading.
This makes it impossible to update the state with get_updated_state AFTER the last record has been emitted.

Describe the solution you’d like

class MyStream:

     @property
     def state(self):
            return {self.cursor_value: "some_date", ...}

    @state.setter
    def state(self, value):
           self._state = parse(value, ...)

in source

     if hasattr(stream, state):
         stream.state = stream_state_value

    ...
    state_checkpoint(stream.state)

Later state attribute could be used to unambiguously detect if the stream is incremental (the current way is to check cursor_field, which is rather weird).