On Wayland, add support for fractional scaling

This adds support for the fractional scaling on Wayland via the
wp-fractional-scale protocol.

Co-authored-by: Julian Orth <ju.orth@gmail.com>

src/platform_impl/linux/mod.rs

@@ -441,7 +441,7 @@ impl Window {
 
     #[inline]
     pub fn scale_factor(&self) -> f64 {
-        x11_or_wayland!(match self; Window(w) => w.scale_factor() as _)
+        x11_or_wayland!(match self; Window(w) => w.scale_factor())
     }
 
     #[inline]