On Windows and MacOS, add Window::has_focus

src/platform_impl/macos/appkit/window.rs

@@ -192,6 +192,9 @@ extern_methods!(
         #[sel(isVisible)]
         pub fn isVisible(&self) -> bool;
 
+        #[sel(isKeyWindow)]
+        pub fn isKeyWindow(&self) -> bool;
+
         #[sel(isZoomed)]
         pub fn isZoomed(&self) -> bool;
 

src/platform_impl/macos/window.rs

@@ -1215,6 +1215,10 @@ impl WinitWindow {
     }
 
     #[inline]
+    pub fn has_focus(&self) -> bool {
+        self.isKeyWindow()
+    }
+
     pub fn set_theme(&self, theme: Option<Theme>) {
         set_ns_theme(theme);
         self.lock_shared_state("set_theme").current_theme = theme.or_else(|| Some(get_ns_theme()));