Implemented focus_window (#1944)

src/platform_impl/windows/window.rs

@@ -685,6 +685,20 @@ impl Window {
     pub fn theme(&self) -> Theme {
         self.window_state.lock().current_theme
     }
+
+    #[inline]
+    pub fn focus_window(&self) {
+        let window = self.window.clone();
+        let window_flags = self.window_state.lock().window_flags();
+
+        let is_visible = window_flags.contains(WindowFlags::VISIBLE);
+        let is_minimized = window_flags.contains(WindowFlags::MINIMIZED);
+        let is_foreground = window.0 == unsafe { winuser::GetForegroundWindow() };
+
+        if is_visible && !is_minimized && !is_foreground {
+            unsafe { force_window_active(window.0) };
+        }
+    }
 }
 
 impl Drop for Window {