[FLINK-35570] Consider PlaceholderStreamStateHandle in checkpoint file merging

[Zakelly]

What is the purpose of the change

In checkpoint file merging, we should take PlaceholderStreamStateHandle into account during lifecycle, since it can be a file merged one.

Brief change log

• take PlaceholderStreamStateHandle into account in reusePreviousStateHandle and couldReuseStateHandle

Verifying this change

This change is already covered by existing tests

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

[flinkbot]

CI report:

• 9f55941 Azure: SUCCESS

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[fredia]

Thanks for the PR, overall LGTM, It would be better if there were more reproducible tests.

[fredia]

IIUC, this bug can be reproduced if we perform several checkpoints before restoring to generate placeholder handle, would you like to change this ITCase to make it easier to reproduce?

[Zakelly]

change to 4 checkpoints per round

[Zakelly]

@flinkbot run azure