[jdk21u-dev] RFR: 8167252: Some of Charset.availableCharsets() does not contain itself

[Goetz Lindenmaier]

I backport this for parity with 21.0.9-oracle

I needed to do a full rebuild to make the change take effect.

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Commit messages:
 - Backport 3eeb681a0de87baa12b6eac5966e7f707b76c8bf

Changes: https://git.openjdk.org/jdk21u-dev/pull/1870/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1870&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8167252
  Stats: 37 lines in 4 files changed: 31 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1870.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1870/head:pull/1870

PR: https://git.openjdk.org/jdk21u-dev/pull/1870