[jdk11u-dev] RFR: 8256110: Create implementation for NSAccessibilityStepper protocol

[Autumn Capasso]

Backport [JDK-8256110](https://bugs.openjdk.org/browse/JDK-8256110) clean backport. One of 28 https://bugs.openjdk.org/browse/JDK-8152350

-------------

Depends on: https://git.openjdk.org/jdk11u-dev/pull/1572

Commit messages:
 - 8256110: Create implementation for NSAccessibilityStepper protocol

Changes: https://git.openjdk.org/jdk11u-dev/pull/1578/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1578&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8256110
  Stats: 131 lines in 5 files changed: 114 ins; 15 del; 2 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1578.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1578/head:pull/1578

PR: https://git.openjdk.org/jdk11u-dev/pull/1578