feat: support macOS menubar (#976)

* feat: macOS menubar

* feat: Dynamic NavigateMenuItems

* fix: simplify shortcut config

* fix: Simplify the code

* fix: More suitable tab name

macos/Runner/AppDelegate.swift

@@ -10,4 +10,19 @@ class AppDelegate: FlutterAppDelegate {
   override func applicationSupportsSecureRestorableState(_ app: NSApplication) -> Bool {
     return true
   }
+
+  override func applicationDidFinishLaunching(_ notification: Notification) {
+    if let controller = mainFlutterWindow?.contentViewController as? FlutterViewController {
+      let channel = FlutterMethodChannel(name: "about", binaryMessenger: controller.engine.binaryMessenger)
+      channel.setMethodCallHandler { (call: FlutterMethodCall, result: @escaping FlutterResult) in
+        if call.method == "showAboutPanel" {
+          NSApp.orderFrontStandardAboutPanel(nil)
+          result(nil)
+        } else {
+          result(FlutterMethodNotImplemented)
+        }
+      }
+    }
+    super.applicationDidFinishLaunching(notification)
+  }
 }