gg: add linux support for fn screen_size() Size fix (#23146)

[islonely]

Fixes #23146 by adding support for Linux users using X11.

_{Huly®: V_0.6-21757}

[spytheman]

This program:

#flag -lX11
#include <X11/Xlib.h>

@[typedef]
pub struct C.Display {}
fn C.XOpenDisplay(int) &C.Display
fn C.XCloseDisplay(display &C.Display) int
fn C.DefaultScreen(&C.Display) int
fn C.DisplayHeight(&C.Display, int) int
fn C.DisplayWidth(&C.Display, int) int

fn main() {
	println('start')
	display := C.XOpenDisplay(0)
	screen := C.DefaultScreen(display)
	dump( C.DisplayWidth(display, screen) )
	dump( C.DisplayHeight(display, screen) )
	C.XCloseDisplay(display)
	println('done')
}

locally produces:

start
[x.v:16] C.DisplayWidth(display, screen): 3840
[x.v:17] C.DisplayHeight(display, screen): 1080
done

I have 2 displays, both with a resolution of 1920x1080, according to xfce4-display-settings:

[spytheman]

If I turn off the second monitor, I get:

start
[x.v:16] C.DisplayWidth(display, screen): 1920
[x.v:17] C.DisplayHeight(display, screen): 1080
done

[islonely]

If I turn off the second monitor, I get:

start
[x.v:16] C.DisplayWidth(display, screen): 1920
[x.v:17] C.DisplayHeight(display, screen): 1080
done

It seems there's not a good quick way to the size of a single screen. I'll be back with a solution soon.

[islonely]

libxrandr-dev is required on ubuntu based systems for this fix.

[spytheman]

Excellent work.