RFR: 8283214: [macos] Screen magnifier does not show the magnified text for JcomboBox [v4]

[Abhishek Kumar]

> The issue exist only for non-editable combobox and the root cause is accessible object is not created due to incorrect index returned from component class which results in no a11y API invoked.
> 
> Proposed solution is to return the correct accessible child from getAccessibleChild method which is AquaComboBoxButton (arrowButton) instance and that results in invoking the a11y APIs to return the current selected item in combobox. 
> 
> Further when the application comes up first time the accessible name is not set for current displayed item in JCombobox that is handled in AquaComboBoxButton which will take care for the current selected item as well as if user modifies the selection by drop-down list.
> 
> CI link is posted in JBS.

Abhishek Kumar has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - set accessiblename to displayed text in JComboBox
 - Merge
 - Explicit frame dispose remove
 - merge
 - Review comment update
 - JComboBox selected item  screen magnifier fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14497/files
  - new: https://git.openjdk.org/jdk/pull/14497/files/1cdc34dc..9fc3e2f8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14497&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14497&range=02-03

  Stats: 14798 lines in 711 files changed: 7200 ins; 3391 del; 4207 mod
  Patch: https://git.openjdk.org/jdk/pull/14497.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14497/head:pull/14497

PR: https://git.openjdk.org/jdk/pull/14497