RFR: 8325566: [TestBug] Util.shutdown() to hide ALL Windows [v2]

[Kevin Rushforth]

On Tue, 19 Mar 2024 22:31:33 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.
>
> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   for each

Marked as reviewed by kcr (Lead).

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PR Review: https://git.openjdk.org/jfx/pull/1407#pullrequestreview-1948793872