RFR: 8355215: Add @spec tags to Emoji related methods

[Naoto Sato]

Adding @spec tags to Emoji related methods in the Character class. A CSR has also been drafted.

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

Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/24779/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24779&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355215
  Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/24779.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24779/head:pull/24779

PR: https://git.openjdk.org/jdk/pull/24779