[FLINK-18034][runtime] Introduce PreferredLocationsRetriever

[zhuzhurk]

What is the purpose of the change

Preferred locations based on state and inputs are scattered into multiple components, which makes it harder to reasoning the calculation and complicates those hosting components.
This PR is to introduce a PreferredLocationsRetriever to be used by ExecutionSlotAllocator which returns preferred locations of an execution vertex and hides the details of the calculation from other components.
This PR is based on #12256.

Brief change log

• Introduced PreferredLocationsRetriever
• Change ExecutionSlotAllocator to use PreferredLocationsRetriever

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): (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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Last check on commit 362a648 (Mon Jun 01 08:31:50 UTC 2020)

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CI report:

• 1a11a1c Azure: FAILURE

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[azagrebin]

Thanks for the PR @zhuzhurk
It looks quite good to me, I have left some smaller comments.
Also, I believe, it would be simpler to merge this as a pre-step for #12256 and base other PRs on it
then we do not need to move the preferred location code again into AbstractExecutionSlotAllocator in #12256.

[azagrebin]

Thanks for addressing the comment @zhuzhurk
I think we can merge this even independently from #12375 (FLINK-17017).

[zhuzhurk]

@azagrebin yes you are right this PR is independent from #12375.
I have rebased it onto the latest master.

[zhuzhurk]

Thanks a lot for the reviewing! @azagrebin
The failed test 'Run Kubernetes test' is due to the broken test env and not related to this PR.
Merging.