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

[Prasanta Sadhukhan]

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

In "Finder" lists, it is always gray
whereas in "Desktop and screensaver", "Extensions", "Network" lists, it follows accent color
I dont see anywhere prominent focus ring is drawn encircling the list cell in native app 
so probably we can just have our JList focused cell follow the accent color in JDK as well without any prominent ring..

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