RFR: 8325566: [TestBug] Util.shutdown() to hide ALL Windows

[Kevin Rushforth]

On Mon, 18 Mar 2024 22:53:03 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> Changing `Util.shutdown()` to hide **all** showing Windows and then call `Platform.exit()`.
> This simplifies the tests and ensures a clean shutdown.

Looks good.

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Marked as reviewed by kcr (Lead).

PR Review: https://git.openjdk.org/jfx/pull/1407#pullrequestreview-1947463852