[FLINK-39073][runtime] Defer alignment check for idle splits

[Efrat19]

What is the purpose of the change

If a split emits watermarks far into the future and then goes idle, alignment check will incorrectly mark it paused.
As max allowed watermark advances, Source operator will transition the split back to active state, (while its still idle)
This change aims to fix the issue by deferring the alignment check for idle splits until they break out of idleness.

Brief change log

1. Tracking currentlyIdleSplits in sourceOperator
2. Avoiding pause of idle splits
3. Adding alignment check when a split switches to not idle to compensate on 2)
4. Improved logging around invalid split transitions

Verifying this change

This change added tests and can be verified. (unitTest)

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: 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:

• b8fc201 Azure: FAILURE

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