Use cfg aliases throught the code base

Co-authored-by: Mads Marquart <mads@marquart.dk>

src/platform_impl/linux/wayland/mod.rs

@@ -1,10 +1,4 @@
-#![cfg(any(
-    target_os = "linux",
-    target_os = "dragonfly",
-    target_os = "freebsd",
-    target_os = "netbsd",
-    target_os = "openbsd"
-))]
+#![cfg(wayland_platform)]
 
 use sctk::reexports::client::protocol::wl_surface::WlSurface;