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

[Ajit Ghaisas]

On Tue, 15 Nov 2022 18:00:59 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

> 1. Introduced the following utility methods:
> - Util.launch
> - Util.shutdown
> - Util.waitForLatch
> 2. Fixed the out-of order calls to Stage.hide() and Platform.exit() in many tests' shutdowns.
> 3. Replaced local waitForLatch copies with Util.waitForLatch

Overall this looks good. Thanks for addressing this.

This is resulting in two test failures when run as a FULL system test run on my macBook with macOS 11.7.1.
- test.javafx.scene.web.ColorChooserTest.testColorChooser()
- test.robot.javafx.scene.ComboBoxTest.testComboBoxSceneChange1()

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