RFR: 8271071 accessibility of a table on macOS lacks cell navigation

[Artem Semenov]

We've extended the current implementation of TableAccessibility to make sure that individual cells are voiced when navigating with the keyboard.

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Commit messages:
 - 8271071 accessibility of a table on macOS lacks cell navigation

Changes: https://git.openjdk.java.net/jdk/pull/5466/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5466&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271071
  Stats: 133 lines in 7 files changed: 63 ins; 70 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5466.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5466/head:pull/5466

PR: https://git.openjdk.java.net/jdk/pull/5466