[jdk21u-dev] RFR: 8319817: Charset constructor should make defensive copy of aliases

[Todd V. Jonker]

Clean backport.

Additional testing:
- [x] New regression test fails without the fix, passes with it
- [x] linux-x86_64-server-release: `JTREG_KEYWORDS="!headful & !external-dep & !printer" make test TEST=all`
    * These tests fail repeatedly, but also fail on `master`:
        * `build/AbsPathsInImage.java`
        * `java/nio/channels/FileChannel/directio/DirectIOTest.java`

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Commit messages:
 - Backport d6d7bdc7748c10963c3e58c0287b2472646bf36f

Changes: https://git.openjdk.org/jdk21u-dev/pull/841/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=841&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319817
  Stats: 76 lines in 2 files changed: 74 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/841.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/841/head:pull/841

PR: https://git.openjdk.org/jdk21u-dev/pull/841