<AWT Dev> RFR: 8256109: Create implementation for NSAccessibilityButton protocol [v6]

[Alexander Zuev]

> Creating a native peer for pushbutton accessibility role on Max OS X.
> The process of choosing of what peer to initialize is clunky so
> might be addressed in the future.

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

  Added AWT_ASSERT_APPKIT_THREAD

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1549/files
  - new: https://git.openjdk.java.net/jdk/pull/1549/files/22fe7535..0b208934

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1549&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1549&range=04-05

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1549.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1549/head:pull/1549

PR: https://git.openjdk.java.net/jdk/pull/1549