RFR: 8362088: CompressedKlassPointers::encode should be const correct

[Thomas Stuefe]

Trivial change. CompressedKlassPointers::encode It should accept a const Klass* .

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Commit messages:
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Changes: https://git.openjdk.org/jdk/pull/26306/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26306&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8362088
  Stats: 8 lines in 2 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/26306.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26306/head:pull/26306

PR: https://git.openjdk.org/jdk/pull/26306