Make WindowBuilder Send + Sync

Window builder is always accessed by winit on the thread event loop
is on, thus it's safe to mark the data it gets as `Send + Sync`.
Each unsafe object is marked individually as `Send + Sync` instead
of just implementing `Send` and `Sync` for the whole builder.

src/platform_impl/linux/wayland/window/mod.rs

@@ -151,7 +151,7 @@ impl Window {
         window_state.set_resizable(attributes.resizable);
 
         // Set startup mode.
-        match attributes.fullscreen.map(Into::into) {
+        match attributes.fullscreen.0.map(Into::into) {
             Some(Fullscreen::Exclusive(_)) => {
                 warn!("`Fullscreen::Exclusive` is ignored on Wayland");
             }