Add an ExtractWindowingInfo transform.

[robertwb]

YAML users don't have access to DoFn params or annotations, so we provide this as an explicit transform.

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[damccorm]

Thanks! Feedback is minor (string fixes), otherwise LGTM.

Please fix linting as well before merging

[damccorm]

(optional, not sure if I like this more) - thoughts on event_timestamp? It might be a little more explicit.

We could even allow a user to specify processing_timestamp (resolves to time.time()) as a convenience.

[robertwb]

Interesting idea.

I'm going to leave it as timestamp. Event timestamps are actually attached to the element, and windows are always in terms of this time. It's also a bit deceptive because if I try to inspect/reify processing time, that's not what will be used when anything else tries to act on it. (In addition, one needs triggers/timers to get into processing time and that's a whole can of worms we don't expose to YAML.)

[codecov]

Codecov Report

Attention: Patch coverage is 89.18919% with 4 lines in your changes missing coverage. Please review.

Project coverage is 57.69%. Comparing base (8031f09) to head (86795a0).
Report is 27 commits behind head on master.

Files with missing lines	Patch %	Lines
sdks/python/apache_beam/yaml/yaml_mapping.py	89.18%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #34051      +/-   ##
============================================
+ Coverage     57.63%   57.69%   +0.06%     
  Complexity     1474     1474              
============================================
  Files           989      993       +4     
  Lines        157126   157354     +228     
  Branches       1076     1076              
============================================
+ Hits          90564    90790     +226     
- Misses        64320    64322       +2     
  Partials       2242     2242              

Flag	Coverage Δ
python	81.27% <89.18%> (+0.05%)	⬆️

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