RFR: 8356983: Create implementation of NSAccessibilityImage protocol

[Alexander Zuev]

- Initial implementation;
- Added accessible text to image view in Ensemble8 to make testing of this feature with Ensemble8 more viable;

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Commit messages:
 - 8356983: Create implementation of NSAccessibilityImage protocol

Changes: https://git.openjdk.org/jfx/pull/1816/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1816&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356983
  Stats: 93 lines in 4 files changed: 91 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1816.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1816/head:pull/1816

PR: https://git.openjdk.org/jfx/pull/1816