Make WindowAttributes private (#2134)

* Make `WindowAttributes` private, and move its documentation

* Reorder WindowAttributes title and fullscreen to match method order

src/platform_impl/macos/mod.rs

@@ -70,7 +70,7 @@ impl Deref for Window {
 }
 
 impl Window {
-    pub fn new<T: 'static>(
+    pub(crate) fn new<T: 'static>(
         _window_target: &EventLoopWindowTarget<T>,
         attributes: WindowAttributes,
         pl_attribs: PlatformSpecificWindowBuilderAttributes,