[FLINK-38998][table] Fix cascaded event time WindowAggregate does not produce data when offset is specified

[sa-kononov]

What is the purpose of the change

This pull request fixes a bug in checking which watermark can fire a window in WindowAggregate operator. An optimization with this check was introduced in #15495 with the function TimeWindowUtils.getNextTriggerWatermark() that did not account for windows with a non-zero offset. As the result it leaded to dropping all but the last window events from cascaded (double) WindowAggregate.

Brief change log

• an offset parameter is added to TimeWindowUtils.getNextTriggerWatermark() and the function is renamed for clarity
• window offset for this is now provided by SliceAssigner interface and its implementations

Verifying this change

Please make sure both new and modified tests in this PR follow the conventions for tests defined in our code quality guide.

This change added tests and can be verified as follows:

• WindowAggregateITCase.testCascadeEventTimeTumbleWindowWithOffset() is modified to cover the relevant case (no need to introduce a new test)

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): don't know
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• 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:

• af8f159 Azure: SUCCESS

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[sa-kononov]

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