RFR: 8329667: [macos] Issue with JTree related fix for JDK-8317771 [v4]

[Alexander Zuev]

> Caching children and selected children of the thee on the native level;
> Caching all children of a specific parent in CAccessibility to enhance recursive children selection algorithm;
> Removing fix for JDK-8317771 as no longer needed;

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

  Replaced NULL with nil in OutlineAccessibility - functionally it has no effect but it is more uiform and according to the ObjectibeC convention where objects are referred as nil and references to the primitives as NULL.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19255/files
  - new: https://git.openjdk.org/jdk/pull/19255/files/6d6cd814..4836a92b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19255&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19255&range=02-03

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/19255.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19255/head:pull/19255

PR: https://git.openjdk.org/jdk/pull/19255