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

jay-config/src/input.rs

@@ -107,6 +107,13 @@ impl Seat {
         Self(raw)
     }
 
+    /// Sets the size of the cursor theme.
+    ///
+    /// Default: 16.
+    pub fn set_cursor_size(self, size: i32) {
+        get!().set_cursor_size(self, size)
+    }
+
     /// Creates a compositor-wide hotkey.
     ///
     /// The closure is invoked when the user presses the last key of the modified keysym.