Re-implement Tooltips in FXGLDefaultMenu using same window for better cross-platform support

[AlmasB]

protected fun createContentAchievements(): MenuContent function of interest.

FXGL/fxgl/src/main/kotlin/com/almasb/fxgl/app/scene/FXGLDefaultMenu.kt

Lines 760 to 764 in 43a1a24

	val tooltip = Tooltip(a.description)
	tooltip.showDelay = Duration.seconds(0.1)
	Tooltip.install(text, tooltip)

In short, we can't use Tooltip because its implementation uses an external Stage.

First, a potential implementation of a tooltip UI object (that is drawn in the same Stage) should be discussed. Eventually, this may go to the UI factory service.