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.rs

@@ -20,6 +20,7 @@ pub mod wl_shm;
 pub mod wl_shm_pool;
 pub mod wl_subcompositor;
 pub mod wl_surface;
+pub mod wp_fractional_scale_manager_v1;
 pub mod wp_presentation;
 pub mod wp_presentation_feedback;
 pub mod wp_viewporter;