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

[Tejesh R]

On Wed, 1 Jun 2022 19:40:34 GMT, Harshitha Onkar <honkar at openjdk.org> wrote:

>> 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

Marked as reviewed by tr (Author).

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