Xlib backend

[Thiago Milczarek Sayão]

Hi,

I got simple samples running on the pure Xlib port of the Gtk backend.

It still has gtk code, but mainly uses Xlib by now. Don't judge the code,
I'm porting it gradually.

https://github.com/openjdk/jfx-sandbox/tree/tsayao_xlib

java @build/run.args -cp apps/toys/Hello/dist/Hello.jar hello.HelloCursors

Window coordinates and sizes are still off a bit, so you might have to
resize the window to redraw.

-- Thiago.