RFR: 8367991: Update RegionBackground tests to use ScreenCaptureTestWatcher utility [v2]

[Kevin Rushforth]

On Fri, 19 Sep 2025 15:46:45 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> Seems like a good idea, but I'd recommend doing it as a separate follow-on bug.
>> 
>> Btw, I would add a `Window... windows` parameter and then this would also be useful for test that only want to close a subset of their windows (some such tests have the main stage remain showing throughout the test and don't want that window closed).
>
> last time I checked, no system test needs to specify which windows to hide.

Maybe not at `@AfterAll` time, but there are tests that close the active window in `@AfterEach` leaving the primary stage shown.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1913#discussion_r2363612579