[FLINK-17330[runtime] Merge cyclic dependent pipelined regions into one region

[zhuzhurk]

What is the purpose of the change

This PR changes regions building to merge cyclic dependent pipelined regions into one region.
This is to avoid scheduling deadlocks due to cyclic dependencies.
More details see FLINK-17330.

Brief change log

• Added StronglyConnectedComponentsComputeUtils to find out cyclic dependent regions
• Changed PipelinedRegionComputeUtil to merge cyclic dependent pipelined regions into one region

Verifying this change

• Added UT StronglyConnectedComponentsComputeUtilsTest
• Added test case in PipelinedRegionComputeUtilTest to verify regions on the same cycles are merged

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

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

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

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Automated Checks

Last check on commit e11ffec (Thu Aug 20 08:33:48 UTC 2020)

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CI report:

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[azagrebin]

Thanks for addressing my comments @zhuzhurk LGTM