Added accessibilityIndex function that correctly returns the index of a child in parent container
------------- Commit messages: - 8208747: [a11y] [macos] In Optionpane Demo, inside ComponentDialog Example, unable to navigate to all items, with VO on Changes: https://git.openjdk.java.net/jdk/pull/4084/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4084&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8208747 Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod Patch: https://git.openjdk.java.net/jdk/pull/4084.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/4084/head:pull/4084 PR: https://git.openjdk.java.net/jdk/pull/4084
