Improve windowing on Wayland

Currently on multi-screen Wayland setups, Minuet opens in a window that is much too big. It stretches across multiple displays in terms of width, and is much too tall as well.

This MR uses Screen.width and Screen.height to set the window size, which should correctly set the display size for the current display on Wayland including if the display is scaled.

There was also a minor change made to maximise the window by default, as this is probably expected if the window is supposed to be the width/height of the screen. Even though maximise is enabled by default, without changing the width/height properties, when the window is "unmaximised" then it becomes too big again.

The maximise change isn't strictly necessary, it's just a quality of life improvement I thought might help. The core change is really to adjust how the width and height is set to improve the experience for Wayland users.