RFR: 8343336: Add persistentScrollBars preference [v4]

[Andy Goryachev]

On Fri, 1 Nov 2024 23:39:51 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

>> This PR adds another accessibility preference that is available on all supported desktop platforms:
>> 
>> 1. **Windows**: Settings -> Accessibility -> Visual Effects -> Always show scroll bars
>> 2. **macOS**: System Settings -> Appearance -> Show scroll bars
>> 3. **Ubuntu**: Settings -> Accessibility -> Seeing -> Always show scroll bars
>> 
>> When the OS setting is changed, all platforms report updates that can be observed in JavaFX.
>> The manual test application `test/manual/events/PlatformPreferencesChangedTest` can be used to test the feature.
>
> Michael Strauß has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Merge branch 'master' into feature/accessibility-hide-scrollbars
>  - add platform keys to javadoc
>  - Change reducedScrollBars to persistentScrollBars
>  - Add reducedScrollBars preference

the code changes look good, and both the property and the key reflect the platform preference on macOS M1 14.7.

I'll test windows tomorrow, and if someone can test it on linux, that would be fantastic!

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PR Review: https://git.openjdk.org/jfx/pull/1618#pullrequestreview-2434706603