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

wire/wp_fractional_scale_v1.txt

@@ -0,0 +1,11 @@
+# requests
+
+msg destroy = 0 {
+
+}
+
+# events
+
+msg preferred_scale = 0 {
+    scale: fixed,
+}