RFR: 8271071 accessibility of a table on macOS lacks cell navigation [v4]

[Artem Semenov]

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

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

  The biggest problem i have is that the new logic reverts the mechanic of the selection mode of the table - when no selection mode set it announces the content of all the cells in the current row and when either row or column selection mode is set it only announces the content of a single cell. Also when only cell selection is allowed it announces row as dimmed which is strange.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5466/files
  - new: https://git.openjdk.java.net/jdk/pull/5466/files/c462fefa..110f4f1a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5466&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5466&range=02-03

  Stats: 768 lines in 13 files changed: 132 ins; 504 del; 132 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