[jdk11u-dev] RFR: 8301119: Support for GB18030-2022

[Andrew John Hughes]

This is the companion implementation change for the recent specification changes which allowed for the additional characters required to support GB18030-2022.

The following modifications were necessary for 11u:

* Manual copyright header changes in `GB18030.java`, `StandardCharsets.java.template` and `ExtendedCharsets.java.template`. 11u is missing JDK-8229960 ("Remove sun.nio.cs.map system property") and, as with 17, JDK-8260265: "UTF-8 by Default", a JEP added in OpenJDK 18
* Manual import statement changes in `ExtendedCharsets.java.template` (`SoftReference` was also unused, removed by JDK-8229960 in 17u)
* Conversion of the `switch` statements to the old style in `GB18030.java` (no Switch Expressions, JEP-361 in OpenJDK 14)
* We retain `stdcs-solaris` and make the same alteration to remove GB18030 as in `stdcs-aix`, `stdcs-linux` and `stdcs-windows`. The Solaris port was not removed until OpenJDK 15 and this file seems to have been overlooked in that removal, until this change.

Tests in `jdk/java/nio/charset` and `jdk/sun/nio/cs` all passed after patching.

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Commit messages:
 - Backport a253b4602147633a3d2e83775d1feef4f12a5272

Changes: https://git.openjdk.org/jdk11u-dev/pull/1897/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1897&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301119
  Stats: 266 lines in 14 files changed: 135 ins; 16 del; 115 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1897.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/1897/head:pull/1897

PR: https://git.openjdk.org/jdk11u-dev/pull/1897