[FLINK-39984][runtime] Dispatch thread dump to ioExecutor

[xingsuo-zbz]

What is the purpose of the change

Fixes FLINK-39984.

Brief change log

Offload the dump to ioExecutor in both TaskExecutor#requestThreadDump and Dispatcher#requestThreadDump via CompletableFuture.supplyAsync, matching the pattern already used by other heavy TE handlers.

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): 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 / docs / JavaDocs / not documented)

[flinkbot]

CI report:

• 6ae3382 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

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

[xingsuo-zbz]

@flinkbot run azure