RFR: 8371860: Make non-pubic methods in java_lang_Class private

[Coleen Phillimore]

Please review this small cleanup for method declarations in java_lang_Class.
Testing with tier1-4.

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Commit messages:
 - 8371860: Make non-pubic methods in java_lang_Class private

Changes: https://git.openjdk.org/jdk/pull/28308/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28308&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371860
  Stats: 25 lines in 2 files changed: 6 ins; 18 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28308.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28308/head:pull/28308

PR: https://git.openjdk.org/jdk/pull/28308