<i18n dev> RFR: 8303018: Unicode Emoji Properties

[Naoto Sato]

Proposing accessor methods to Emoji properties defined in [Unicode Technical Standard #51](https://unicode.org/reports/tr51/) in `java.lang.Character` class. This is per a request from the client group, as well as refining the currently existing ad-hoc emoji implementation in regex. A CSR has also been drafted, and I would appreciate reviews for it too.

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Commit messages:
 - Clean-up
 - UTR -> UTS
 - prepared javadoc
 - added a test case
 - 8303018: Unicode Emoji Properties

Changes: https://git.openjdk.org/jdk/pull/13006/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13006&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303018
  Stats: 869 lines in 19 files changed: 592 ins; 254 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/13006.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13006/head:pull/13006

PR: https://git.openjdk.org/jdk/pull/13006