RFR: 8343336: Add persistentScrollBars preference

[Michael Strauß]

On Thu, 31 Oct 2024 03:56:30 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.

Changed the naming from `reducedScrollBars` to `persistentScrollBars`, as this matches the logic of the OS settings more closely.

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

PR Comment: https://git.openjdk.org/jfx/pull/1618#issuecomment-2450791817