[jdk11u-ri] RFR: 8305682: Update the javadoc in the Character class to state support for GB 18030-2022 Implementation Level 2

[Naoto Sato]

This is to support GB18030-2022 "Implementation Level 2", an extension to [JDK-8301401](https://bugs.openjdk.org/browse/JDK-8301401). Although all the required code points for Implementation Level 2 are included in JDK 11, the javadoc in the Character class needs to be changed.

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Commit messages:
 - 8305682: Update the javadoc in the Character class to state support for GB 18030-2022 Implementation Level 2

Changes: https://git.openjdk.org/jdk11u-ri/pull/8/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-ri&pr=8&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305682
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk11u-ri/pull/8.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-ri.git pull/8/head:pull/8

PR: https://git.openjdk.org/jdk11u-ri/pull/8