RFR: 8301119: Support for GB18030-2022 [v4]

[Naoto Sato]

> Upgrading the GB18030 charset in the JDK to the latest 2022 standard. Since this is not a compatible upgrade to the existing mapping, a new system property `jdk.charset.GB18030` is introduced. If it is set to "2000", the mapping falls back to the existing mapping based on the 2000 standard, otherwise, it defaults to 2022 mapping. Refer to the corresponding CSR for more detail.

Naoto Sato has updated the pull request incrementally with two additional commits since the last revision:

 - Failed to add the file itself
 - Changed GB18030 from extcs template to stdcs source

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12518/files
  - new: https://git.openjdk.org/jdk/pull/12518/files/4d4015a9..9732e6c8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12518&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12518&range=02-03

  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12518.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12518/head:pull/12518

PR: https://git.openjdk.org/jdk/pull/12518