[FLINK-23809][checkpoint] Respect the finished flag when extracting operator states due to skip in-flight data

[gaoyunhaii]

What is the purpose of the change

This PR fixes that when enabled skipping in-flight data, the checkpoint coordinator would create new OperatorState but discard the in-flight data, but it does not consider the finished flag for now.

Brief change log

• 2b37118 fixes the issue by considering the finished flag.

Verifying this change

This change is verified by the added UT.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: yes
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Automated Checks

Last check on commit 2b37118 (Fri Aug 20 15:09:24 UTC 2021)

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CI report:

• b97d86d Azure: SUCCESS

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[pnowojski]

Thanks for the fix @gaoyunhaii . Change makes sense to me. I've added one comment to help avoid this kind of issues in the future.

[gaoyunhaii]

Very thanks Piotr @pnowojski for the review! I modified the code according to the comments~

[pnowojski]

LGTM, thanks for the update @gaoyunhaii

[gaoyunhaii]

Very thanks Piotr @pnowojski for the review! I'll merge the code~