[jdk21u-dev] RFR: 6928542: Chinese characters in RTF are not decoded

[Ichiroh Takiguchi]

Backport [JDK-6928542](https://bugs.openjdk.org/browse/JDK-6928542) Chinese characters in RTF are not decoded
Cherry-pick worked fine as expected.

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Commit messages:
 - Backport a26f7c03c72e4efe6d3219d294294c5

Changes: https://git.openjdk.org/jdk21u-dev/pull/46/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=46&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-6928542
  Stats: 286 lines in 3 files changed: 282 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/46.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/46/head:pull/46

PR: https://git.openjdk.org/jdk21u-dev/pull/46