Desktop: Hook up native window controls (#3161)

* Implement window controls

* Fix drag target size

* Maximize with drag area double click

editor/src/messages/app_window/app_window_message.rs

@@ -8,5 +8,6 @@ pub enum AppWindowMessage {
 	AppWindowMinimize,
 	AppWindowMaximize,
 	AppWindowUpdatePlatform { platform: AppWindowPlatform },
+	AppWindowDrag,
 	AppWindowClose,
 }

editor/src/messages/app_window/app_window_message_handler.rs

@@ -31,6 +31,9 @@ impl MessageHandler<AppWindowMessage, ()> for AppWindowMessageHandler {
 				self.platform = platform;
 				responses.add(FrontendMessage::UpdatePlatform { platform: self.platform });
 			}
+			AppWindowMessage::AppWindowDrag => {
+				responses.add(FrontendMessage::DragWindow);
+			}
 			AppWindowMessage::AppWindowClose => {
 				responses.add(FrontendMessage::CloseWindow);
 			}

editor/src/messages/frontend/frontend_message.rs

@@ -343,6 +343,7 @@ pub enum FrontendMessage {
 		maximized: bool,
 		minimized: bool,
 	},
+	DragWindow,
 	CloseWindow,
 	UpdateViewportHolePunch {
 		active: bool,