[in_app_purchase] Update country code Android example (flutter#6722)

Updates the Android example app to use the replacement for the deprecated `getCountryCode`. Also udpates the deprecations method for `getCountryCode` to point to the correct variant of the platform interface method.

Follow-up to flutter/flutter#147230

Author: stuartmorgan-g

packages/in_app_purchase/in_app_purchase_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.3.5+1
+
+* Updates example to use `countryCode` instead of deprecated `getCountryCode`.
+
 ## 0.3.5
 
 * Replaces `getCountryCode` with `countryCode`.

packages/in_app_purchase/in_app_purchase_android/example/lib/main.dart

@@ -259,10 +259,7 @@ class _MyAppState extends State<_MyApp> {
           foregroundColor: Colors.white,
         ),
         onPressed: () {
-          final InAppPurchaseAndroidPlatformAddition addition =
-              InAppPurchasePlatformAddition.instance!
-                  as InAppPurchaseAndroidPlatformAddition;
-          unawaited(deliverCountryCode(addition.getCountryCode()));
+          unawaited(deliverCountryCode(_inAppPurchasePlatform.countryCode()));
         },
         child: const Text('Fetch Country Code'),
       ),

packages/in_app_purchase/in_app_purchase_android/lib/src/in_app_purchase_android_platform_addition.dart

@@ -167,7 +167,7 @@ class InAppPurchaseAndroidPlatformAddition
   ///
   /// See: https://developer.android.com/reference/com/android/billingclient/api/BillingConfig
   /// See: https://unicode.org/cldr/charts/latest/supplemental/territory_containment_un_m_49.html
-  @Deprecated('Use InAppPurchasePlatfrom.getCountryCode')
+  @Deprecated('Use InAppPurchasePlatfrom.countryCode')
   Future<String> getCountryCode() async {
     final BillingConfigWrapper billingConfig = await _billingClientManager
         .runWithClient((BillingClient client) => client.getBillingConfig());

packages/in_app_purchase/in_app_purchase_android/pubspec.yaml

@@ -2,7 +2,7 @@ name: in_app_purchase_android
 description: An implementation for the Android platform of the Flutter `in_app_purchase` plugin. This uses the Android BillingClient APIs.
 repository: https://github.com/flutter/packages/tree/main/packages/in_app_purchase/in_app_purchase_android
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+in_app_purchase%22
-version: 0.3.5
+version: 0.3.5+1
 
 environment:
   sdk: ^3.1.0