RFR: JDK-8287261: [macos] JList Focus Ring color doesn't follow Accent color changes on macOS [v2]

[Harshitha Onkar]

> With the proposed fix, JList's focus ring color follows accent color changes. Previously the focus ring for JList was not prominently visible and did not follow accent color changes.
> 
> While investing a similar issue related to JTable (https://github.com/openjdk/jdk/pull/7768#discussion_r839813517), it was observed that List.focusCellHighlightBorder was using the cellFocusRing color as well. This PR extends the focus ring accent color changes to JLists. 
> 
> Related issues: [JDK-7124282](https://bugs.openjdk.java.net/browse/JDK-7124282) , [JDK-8261243](https://bugs.openjdk.java.net/browse/JDK-8261243)
> 
> ####    Summary of changes
> 
> -  focusCellHighlightBorder in `AquaLookAndFeel` changed which is used for cell border for lists and tables
> -  code related to on-the-fly focus ring color refactored into a separate method (`changeFocusRingColor()`) for re-usability 
> -  `changeFocusRingColor()` called when PropertyChangeEvent == FRAME_ACTIVE_PROPERTY and the frame gains focus, instead of calling in individual `swapSelectionColors` in `AquaFocusHandler.java`
> - Common test added - `CellFocusRingTest`, which tests for both cases - Tables & Lists. 
> 
> **Before and After screenshots of JList** _(Screenshots from SwingSet2 demo)_
> 
> ![Screen Shot 2022-05-25 at 3 55 49 PM](https://user-images.githubusercontent.com/95945681/170382727-54ed155b-6f08-4c75-8657-89c15764e1cd.png)

Harshitha Onkar has updated the pull request incrementally with one additional commit since the last revision:

  removed redundant null checks in test

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8896/files
  - new: https://git.openjdk.java.net/jdk/pull/8896/files/54e54719..e98484fe

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8896&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8896&range=00-01

  Stats: 110 lines in 2 files changed: 40 ins; 55 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8896.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8896/head:pull/8896

PR: https://git.openjdk.java.net/jdk/pull/8896