Make WindowAttributes private (#2134)

* Make `WindowAttributes` private, and move its documentation

* Reorder WindowAttributes title and fullscreen to match method order

src/platform_impl/macos/window.rs

@@ -371,7 +371,7 @@ unsafe impl Send for UnownedWindow {}
 unsafe impl Sync for UnownedWindow {}
 
 impl UnownedWindow {
-    pub fn new(
+    pub(crate) fn new(
         mut win_attribs: WindowAttributes,
         pl_attribs: PlatformSpecificWindowBuilderAttributes,
     ) -> Result<(Arc<Self>, IdRef), RootOsError> {