RFR: 8361379: [macos] Refactor accessibility code to retrieve attribute by name

[Alexander Zuev]

- Copyright year update;
- Introduce new function requestNodeAttribute and refactor code to use it;
- Fix some typos;
- Enable new code to handle TabPages since TabGroup was implemented;

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Commit messages:
 - 8361379: [macos] Refactor accessibility code to retrieve attribute by name

Changes: https://git.openjdk.org/jfx/pull/1840/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1840&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361379
  Stats: 94 lines in 3 files changed: 12 ins; 54 del; 28 mod
  Patch: https://git.openjdk.org/jfx/pull/1840.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1840/head:pull/1840

PR: https://git.openjdk.org/jfx/pull/1840