<i18n dev> RFR: 8301119: Support for GB18030-2022 [v2]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 16 additional commits since the last revision:

 - Add @Stable annotation
 - Merge branch 'master' into JDK-8301119-GB18030-2022
 - Check initPhase and don't call System.getProperty if in phase 1
 - Some clean-up
 - Some more fixes
 - removed unnecessary method name composition
 - Removed unnecessary imports
 - aliases fix
 - Move GB18030 into standard charsets provider
 - indentation
 - ... and 6 more: https://git.openjdk.org/jdk/compare/0981ec17...b5379b69

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/12518/files
  - new: https://git.openjdk.org/jdk/pull/12518/files/0f3c25ce..b5379b69

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12518&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12518&range=00-01

  Stats: 8209 lines in 333 files changed: 4912 ins; 1488 del; 1809 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