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

[Jayathirth D V]

On Mon, 22 Sep 2025 11:55:16 GMT, Jayathirth D V <jdv at openjdk.org> wrote:

>> 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.

Follow-up issue : [JDK-8368363](https://bugs.openjdk.org/browse/JDK-8368363)

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PR Review Comment: https://git.openjdk.org/jfx/pull/1913#discussion_r2371255041