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/ifs/wl_surface/xdg_surface.rs

@@ -124,6 +124,7 @@ impl XdgSurface {
 
     fn set_workspace(&self, ws: &Rc<WorkspaceNode>) {
         self.workspace.set(Some(ws.clone()));
+        self.surface.set_output(&ws.output.get());
         let pu = self.popups.lock();
         for pu in pu.values() {
             pu.xdg.set_workspace(ws);