[FLINK-6258] Deprecate ListCheckpointed interface

[aljoscha]

This also updates the documentation and changes usage in our code to
CheckpointedFunction.

The Google PubSub source unfortunately also uses ListCheckpointed but
here we cannot migrate to CheckpointedFunction because of savepoint
compatibility.

Brief change log

• add @deprecated annotation, pointing to CheckpointedFunction as the replacement
• migrate documentation and examples and internal usage
• there is one usage left in the GCP PubSub connector, we cannot change that because of savepoint compatibility

Verifying this change

• this change some tests to use CheckpointedFunction instead of ListCheckpointed

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): ListCheckpointed is @PublicEvolving
• 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/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

Documentation is updated to remove mentions of ListCheckpointed.

cc @knaufk @sjwiesman @alpinegizmo @NicoK (it's probably good for you to be aware of this). Could one of you maybe give me a review?

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Automated Checks

Last check on commit d0915b5 (Thu Apr 02 11:08:52 UTC 2020)

Warnings:

• Documentation files were touched, but no .zh.md files: Update Chinese documentation or file Jira ticket.

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[sjwiesman]

@aljoscha this looks good to me. You could replace the usage in the pubsub connector my using the same state descriptor as ListCheckpointed. The only caveat is JavaSerializer is currently package-private so that would also need to be changed. Your choice if you want to address that or not.

new ListStateDescriptor<>("_default_", new JavaSerializer<>());

Also, can you please open a follow-up ticket to update the Chinese docs.

[sjwiesman]

Just thinking out loud, not for this pr, but we are probably going to need to update the data stream docs to avoid the phrase "stateful function"

[aljoscha]

😂

[aljoscha]

Yes, I didn't want to go into extra shenanigans with JavaSerializer. I think that class also should not exist... 🙈

[aljoscha]

But otherwise you think it's good to merge? I would create a Jira issue for the chinese doc and point at the commit that does this change here.

[sjwiesman]

👍 to merge