RFR: 8329705: Add missing Application thread checks to platform specific a11y methods

[Alexander Zuev]

Added missing checks;
Added a manual regression test;

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Commit messages:
 - 8329705: Add missing Application thread checks to platform specific a11y methods
 - Merge pull request #8 from openjdk/master
 - Merge pull request #7 from openjdk/master

Changes: https://git.openjdk.org/jfx/pull/1436/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1436&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329705
  Stats: 299 lines in 4 files changed: 299 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1436.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1436/head:pull/1436

PR: https://git.openjdk.org/jfx/pull/1436