[FLINK-31261][runtime] Make AdaptiveScheduler aware of local state size

[rkhachatryan]

What is the purpose of the change

FLINK-21450 / #21981 made Adaptive Scheduler aware of Local State. This PR improves on that by estimating state size (instead of number of key groups).

Verifying this change

• Added unit test: StateLocalitySlotAssignerTest.testDownScaleWithUnevenStateSize

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, 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? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• c2b1e6528193b33cc6d38237b70b4b844539f1ab Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[rkhachatryan]

Thanks for the review! Given https://github.com/apache/flink/pull/22046#discussion_r1681407852, I think the improvement should be significant but not in all cases.