RFR: 8298645 JNI works with accessibleSelection on a wrong thread [v2]

[Artem Semenov]

> [ComboBoxAccessibility accessibilityValue] works with the accessibleSelection object directly, however the work should go through CAccessibility so that it is executed on the Event Dispatch thread.

Artem Semenov has updated the pull request incrementally with one additional commit since the last revision:

  A comment or javadoc should mention that this is called from native code, specifically pointing to ComboBoxAccessibility.m.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11653/files
  - new: https://git.openjdk.org/jdk/pull/11653/files/077b215e..38319bf7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11653&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11653&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11653.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11653/head:pull/11653

PR: https://git.openjdk.org/jdk/pull/11653