MINOR: Cleanup simplify set initialization with Set.of

[Yunyung]

Simplify Set initialization and reduce the overhead of creating extra
collections.

The changes mostly include:

• new HashSet<>(List.of(...))
• new HashSet<>(Arrays.asList(...)) / new HashSet<>(asList(...))
• new HashSet<>(Collections.singletonList()) / new
  HashSet<>(singletonList())
• new HashSet<>(Collections.emptyList())
• new HashSet<>(Set.of())

This change takes the following into account, and we will not change to
Set.of in these scenarios:

• Require mutability (UnsupportedOperationException).
• Allow duplicate elements (IllegalArgumentException).
• Allow null elements (NullPointerException).
• Depend on Ordering. Set.of does not guarantee order, so it could
  make tests flaky or break public interfaces.

Reviewers: Ken Huang s7133700@gmail.com, PoAn Yang
payang@apache.org, Chia-Ping Tsai chia7712@gmail.com

[Yunyung]

kafka/connect/runtime/src/test/java/org/apache/kafka/connect/runtime/WorkerSinkTaskTest.java

Lines 137 to 138 in 8fd0d33

	private static final Set<TopicPartition> INITIAL_ASSIGNMENT =
	new HashSet<>(Arrays.asList(TOPIC_PARTITION, TOPIC_PARTITION2));

Keep the above line unchanged to avoid flaky in the verify(...) below:

kafka/connect/runtime/src/test/java/org/apache/kafka/connect/runtime/WorkerSinkTaskTest.java

Line 1535 in 8fd0d33

verify(sinkTask).close(new ArrayList<>(workerCurrentOffsets.keySet()));

[Yunyung]

Also remove unnecessary duplicates t1p0, t2p0.

[FrankYang0529]

Thanks for the PR.

Could you also change new HashSet<>(Collections.singletonList()) to Set.of()?

[m1a2st]

Thank @Yunyung for this patch, left a comment.

• ClassicGroupTest L423 also can update

[Yunyung]

Thanks @FrankYang0529 and @m1a2st for the review. Update according to the comments.