RFR: 8206430: Use consistent pattern for startup in FX system tests [v4]

[Kevin Rushforth]

On Wed, 16 Nov 2022 18:06:21 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> 1. added a method with 15 second default.  There are only 4 remaining that use custom timeout, the first two use 5, the other two 50:
>> test.javafx.embed.swing.JFXPanelTest.doSetupOnce()
>> test.javafx.embed.swing.SwingFXUtilsTest.doSetupOnce()
>> test.javafx.embed.swing.SwingNodeMemoryLeakTest.setupOnce()
>> test.javafx.embed.swing.SwingNodeScaleTest.setupOnce()
>
> 2. will add Util.startup(CountDownLatch, Runnable) for some of the tests

> There are only 4 remaining that use custom timeout, the first two use 5, the other two 50

The ones using 5 seconds are mistakes (so they can use the variant without the explicit timeout). Not sure whether the ones that use 50 need to, but it seems safest to leave them alone.

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PR: https://git.openjdk.org/jfx/pull/950