Add setWindowOrigin command

[slipher]

Could be useful in scripting automatic testing and stuff. I can put it at, say, (-2000 -2000) to make the window not visible. (Tested on Windows; not sure if that works on all systems.)

[DolceTriade]

We should probably test this elsewhere

[slipher]

Now tested. On Linux (KDE, Wayland), it works. You can place the window completely off-screen in any direction.
On Mac it also works. The window can't be moved past the top of the screen (y is clamped to 0). It can be placed partially off the 3 other sides but is clamped at the point where just a little bit of the window remains on-screen.

On all systems, screenshots work even if the window is offscreen. (This was a concern for me even since screenshots while minimized often don't work.)