wayland: implement scaling

This involves many subsystems:

- config:
    - allow setting the connector scale
    - allow setting the cursor size
- cursors:
    - load server cursors for all requested sizes and scales
- wl_surface:
    - track the output the surface belongs to
    - send wl_surface.enter/leave
- wl_output:
    - implement wl_output.scale
- text:
    - pre-render texts for all used scales
- renderer:
    - properly align scale textures and rectangles
- wp_fractional_scale:
    - new interface for fractional scaling

src/xwayland/xwm.rs

@@ -424,6 +424,10 @@ impl Wm {
                 Some(f) => f,
                 _ => break 'set_root_cursor,
             };
+            let first = match first.iter().find(|i| i.0 .0 == 1) {
+                Some(f) => f.1,
+                _ => break 'set_root_cursor,
+            };
             let cursor = match c
                 .create_cursor(
                     &first.pixels,