RFR: 8351357: Add canary system test checking if Stage receives focus on show [v2]

[Lukasz Kostyra]

On Tue, 17 Jun 2025 15:18:17 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> A delay of some sort is necessary to give the event loop time to process the event.
>
> Right. I think Andy was suggesting a latch (with a timeout) that would be triggered (counted down to 0) when the event was received. This would also remove the concern I raised about the flag not being volatile.

With a latch I think we don't even need the boolean value (we can simply wait for latch to trigger) so I removed it

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PR Review Comment: https://git.openjdk.org/jfx/pull/1804#discussion_r2154198905