Spring Use toUnmodifiableSet and toList instead of collectingAndThen

As Spring Framework 6 uses JDK17 for its baseline, we can make use of toList() and toUnmodifiableSet() which introduced in JDK 16 and JDK 10 respectively.

Comment From: pivotal-cla

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Comment From: pivotal-cla

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Comment From: sbrannen

This has been merged into main.

Thanks