Allow introspection of WindowBuilder attributes

Makes WindowAttributes public and adds window_attributes() getter to
WindowBuilder.

In version 0.27, the WindowAttributes struct was made private, but this
removed the ability to introspect the default WindowBuilder values.

src/platform_impl/ios/view.rs

@@ -455,7 +455,7 @@ impl WinitUIWindow {
 
         this.setRootViewController(Some(view_controller));
 
-        match window_attributes.fullscreen {
+        match window_attributes.fullscreen.clone().map(Into::into) {
             Some(Fullscreen::Exclusive(ref video_mode)) => {
                 let monitor = video_mode.monitor();
                 let screen = monitor.ui_screen();

src/platform_impl/ios/window.rs

@@ -416,7 +416,8 @@ impl Window {
         // TODO: transparency, visible
 
         let main_screen = UIScreen::main(mtm);
-        let screen = match window_attributes.fullscreen {
+        let fullscreen = window_attributes.fullscreen.clone().map(Into::into);
+        let screen = match fullscreen {
             Some(Fullscreen::Exclusive(ref video_mode)) => video_mode.monitor.ui_screen(),
             Some(Fullscreen::Borderless(Some(ref monitor))) => monitor.ui_screen(),
             Some(Fullscreen::Borderless(None)) | None => &main_screen,

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

@@ -240,7 +240,7 @@ impl Window {
         window.set_title(attributes.title);
 
         // Set fullscreen/maximized if so was requested.
-        match attributes.fullscreen {
+        match attributes.fullscreen.map(Into::into) {
             Some(Fullscreen::Exclusive(_)) => {
                 warn!("`Fullscreen::Exclusive` is ignored on Wayland")
             }

src/platform_impl/linux/x11/window.rs

@@ -484,7 +484,8 @@ impl UnownedWindow {
                 window.set_maximized_inner(window_attrs.maximized).queue();
             }
             if window_attrs.fullscreen.is_some() {
-                if let Some(flusher) = window.set_fullscreen_inner(window_attrs.fullscreen.clone())
+                if let Some(flusher) =
+                    window.set_fullscreen_inner(window_attrs.fullscreen.clone().map(Into::into))
                 {
                     flusher.queue()
                 }

src/platform_impl/macos/window.rs

@@ -217,7 +217,7 @@ impl WinitWindow {
         }
 
         let this = autoreleasepool(|_| {
-            let screen = match &attrs.fullscreen {
+            let screen = match attrs.fullscreen.clone().map(Into::into) {
                 Some(Fullscreen::Borderless(Some(monitor)))
                 | Some(Fullscreen::Exclusive(VideoMode { monitor, .. })) => {
                     monitor.ns_screen().or_else(NSScreen::main)
@@ -459,7 +459,7 @@ impl WinitWindow {
         let delegate = WinitWindowDelegate::new(&this, attrs.fullscreen.is_some());
 
         // Set fullscreen mode after we setup everything
-        this.set_fullscreen(attrs.fullscreen);
+        this.set_fullscreen(attrs.fullscreen.map(Into::into));
 
         // Setting the window as key has to happen *after* we set the fullscreen
         // state, since otherwise we'll briefly see the window at normal size

src/platform_impl/windows/window.rs

@@ -1011,7 +1011,7 @@ impl<'a, T: 'static> InitData<'a, T> {
         win.set_enabled_buttons(attributes.enabled_buttons);
 
         if attributes.fullscreen.is_some() {
-            win.set_fullscreen(attributes.fullscreen);
+            win.set_fullscreen(attributes.fullscreen.map(Into::into));
             force_window_active(win.window.0);
         } else {
             let size = attributes