Add-to-app iOS flutter_post_install post_install hook (#1079)

add_to_app/books/ios_books/Podfile

@@ -10,3 +10,7 @@ target 'IosBooks' do
   # Pods for IosBooks
   install_all_flutter_pods(flutter_application_path)
 end
+
+post_install do |installer|
+  flutter_post_install(installer) if defined?(flutter_post_install)
+end

add_to_app/fullscreen/ios_fullscreen/Podfile

@@ -22,3 +22,7 @@ target 'IOSFullScreen' do
   end
 
 end
+
+post_install do |installer|
+  flutter_post_install(installer) if defined?(flutter_post_install)
+end

add_to_app/multiple_flutters/multiple_flutters_ios/Podfile

@@ -9,3 +9,7 @@ target 'MultipleFluttersIos' do
   use_frameworks!
   install_all_flutter_pods(flutter_application_path)
 end
+
+post_install do |installer|
+  flutter_post_install(installer) if defined?(flutter_post_install)
+end

add_to_app/plugin/ios_using_plugin/Podfile

@@ -20,5 +20,8 @@ target 'IOSUsingPlugin' do
     inherit! :search_paths
     # Pods for testing
   end
+end
 
+post_install do |installer|
+  flutter_post_install(installer) if defined?(flutter_post_install)
 end