Setup to handle app window on desktop (#1028)

provider_shopper/windows/flutter/generated_plugin_registrant.cc

@@ -0,0 +1,14 @@
+//
+//  Generated file. Do not edit.
+//
+
+// clang-format off
+
+#include "generated_plugin_registrant.h"
+
+#include <window_size/window_size_plugin.h>
+
+void RegisterPlugins(flutter::PluginRegistry* registry) {
+  WindowSizePluginRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("WindowSizePlugin"));
+}