RFR: 8313556: Create implementation of NSAccessibilitySlider protocol [v8]

[Alexander Zuev]

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

Alexander Zuev has updated the pull request incrementally with one additional commit since the last revision:

  Remove duplicate code make accessibilityLabel explicitly call accessibilityTitle and add coment explaining why.

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1226/files
  - new: https://git.openjdk.org/jfx/pull/1226/files/09f68099..1ae393ac

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1226&range=07
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1226&range=06-07

  Stats: 6 lines in 1 file changed: 0 ins; 3 del; 3 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