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/globals.rs

@@ -18,6 +18,7 @@ use {
             },
             wl_shm::WlShmGlobal,
             wl_subcompositor::WlSubcompositorGlobal,
+            wp_fractional_scale_manager_v1::WpFractionalScaleManagerV1Global,
             wp_presentation::WpPresentationGlobal,
             wp_viewporter::WpViewporterGlobal,
             xdg_wm_base::XdgWmBaseGlobal,
@@ -143,6 +144,7 @@ impl Globals {
         add_singleton!(ZwpRelativePointerManagerV1Global);
         add_singleton!(ExtSessionLockManagerV1Global);
         add_singleton!(WpViewporterGlobal);
+        add_singleton!(WpFractionalScaleManagerV1Global);
 
         if backend.supports_idle() {
             add_singleton!(ZwpIdleInhibitManagerV1Global);