RFR: 8302687 Implement interfaces and shared code for announcement feature [v3]

[Artem Semenov]

> This enhancement covers basic API and shared code that should be implemented for the Accessibility Announcement feature.
> 
> CSR [JDK-8304499](https://bugs.openjdk.org/browse/JDK-8304499 "bugs.openjdk.org")
> 
> @mrserb @prrace @azuev-java please review

Artem Semenov has updated the pull request incrementally with one additional commit since the last revision:

  Minor: no newline at the last line of the file. Not an error just a cosmetic.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13001/files
  - new: https://git.openjdk.org/jdk/pull/13001/files/1e8fe769..9d770ebb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13001&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13001&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13001.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13001/head:pull/13001

PR: https://git.openjdk.org/jdk/pull/13001