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

[Jayathirth D V]

On Fri, 19 Sep 2025 16:48:09 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> Maybe not at `@AfterAll` time, but there are tests that close the active window in `@AfterEach` leaving the primary stage shown.
>
> Anyway, this is another reason why this should be a follow-up issue: so we can discuss the requirements of a more general utility.

I will leave this update to `test.util.Util` for follow up issue.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1913#discussion_r2367936643