RFR: 8313556: Create implementation of NSAccessibilitySlider protocol

[Alexander Zuev]

Create implementation for Slider and Stepper accessibility protocols.
Fix mapping.
Fix performAction parameter type in declaration.

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Commit messages:
 - 8313556:  Create implementation of NSAccessibilitySlider protocol

Changes: https://git.openjdk.org/jfx/pull/1226/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1226&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313556
  Stats: 199 lines in 6 files changed: 197 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1226.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1226/head:pull/1226

PR: https://git.openjdk.org/jfx/pull/1226