RFR: 8333774: Avoid eagerly loading various EmptySpliterator classes

[Claes Redestad]

Trivially move a few private static finals to their respective source type to avoid eagerly loading a few small classes.

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Commit messages:
 - 8333774: Avoid eagerly loading various EmptySpliterator classes

Changes: https://git.openjdk.org/jdk/pull/19591/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19591&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333774
  Stats: 31 lines in 1 file changed: 12 ins; 11 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/19591.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19591/head:pull/19591

PR: https://git.openjdk.org/jdk/pull/19591