potential groovy-groovyfx optional module

[Paul King]

Hi folks,

I have a PR (against an old issue) that provides support for a nice
DSL over JavaFX:

https://github.com/apache/groovy/pull/2989

I followed some design advice from Andres (and AI) to keep maintenance
low. It provides a SwingBuilder style experience:

GroovyFX.start {
    stage(title: 'Hello', show: true) {
        scene(width: 300, height: 100) {
            vbox(spacing: 10, padding: 10) {
                button('Click me', onAction: { println 'clicked' })
            }
        }
    }
}

It also has the normal bells and whistles you might expect, e.g.:

lineChart {
    series('Sales', data: [[1, 10], [2, 14], [3, 9]])
    series('Costs', data: [Jan: 4, Feb: 5])
}

Any feedback welcome (thanks for comments so far Daniel). Is the name
okay, or should we shorten it to groovy-fx?

Currently, the implementation intentionally doesn't bring the
transitive dependencies into the standard install. So you might need a
JDK with JavaFX bundled or add a @Grab if you plan to play with it;
normal Maven/Gradle dependencies should also provide what you need.

Cheers, Paul.