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/screenshoter.rs

@@ -1,5 +1,6 @@
 use {
     crate::{
+        fixed::Fixed,
         format::XRGB8888,
         render::RenderError,
         state::State,
@@ -59,6 +60,7 @@ pub fn take_screenshot(state: &State) -> Result<Screenshot, ScreenshooterError>
         Some(state.root.extents.get()),
         false,
         &mut Default::default(),
+        Fixed::from_int(1),
     );
     let drm = ctx.gbm.drm.dup_render()?.fd().clone();
     Ok(Screenshot { drm, bo })