RFR: 8179918: EnumSet spliterator should report SORTED, ORDERED, NONNULL

[Patrick Strawderman]

I noticed that the Spliterator for EnumSet does not report SORTED, ORDERED, or NONNULL characteristics, all of which are inherent to API of EnumSet. I found there's an existing ticket for this as well.

The ticket also mentions optimized `forEach`, etc, which I presume means avoiding the default implementation that uses the iterator and just iterating over the bitset directly; I can add that here or perhaps in a follow up if it's still deemed worthwhile.

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Commit messages:
 - 8179918: EnumSet spliterator should report SORTED, ORDERED, NONNULL

Changes: https://git.openjdk.org/jdk/pull/28568/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28568&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8179918
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28568.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28568/head:pull/28568

PR: https://git.openjdk.org/jdk/pull/28568