test that flutter_rust_bridge works

flutter_app/macos/Runner/AppDelegate.swift

@@ -0,0 +1,9 @@
+import Cocoa
+import FlutterMacOS
+
+@NSApplicationMain
+class AppDelegate: FlutterAppDelegate {
+  override func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
+    return true
+  }
+}