Intial add of country code, no tests

packages/in_app_purchase/in_app_purchase_android/android/build.gradle

@@ -29,7 +29,7 @@ android {
     compileSdkVersion 33
 
     defaultConfig {
-        minSdkVersion 16
+        minSdkVersion 19
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
     }
     lintOptions {
@@ -61,7 +61,7 @@ dependencies {
     // org.jetbrains.kotlin:kotlin-bom artifact purpose is to align kotlin stdlib and related code versions.
     // See: https://youtrack.jetbrains.com/issue/KT-55297/kotlin-stdlib-should-declare-constraints-on-kotlin-stdlib-jdk8-and-kotlin-stdlib-jdk7
     implementation(platform("org.jetbrains.kotlin:kotlin-bom:1.8.22"))
-    implementation 'com.android.billingclient:billing:6.0.1'
+    implementation 'com.android.billingclient:billing:6.1.0'
     testImplementation 'junit:junit:4.13.2'
     testImplementation 'org.json:json:20231013'
     testImplementation 'org.mockito:mockito-core:5.4.0'

packages/in_app_purchase/in_app_purchase_android/android/src/main/java/io/flutter/plugins/inapppurchase/MethodCallHandlerImpl.java

@@ -20,6 +20,8 @@
 import androidx.annotation.VisibleForTesting;
 import com.android.billingclient.api.AcknowledgePurchaseParams;
 import com.android.billingclient.api.BillingClient;
+import com.android.billingclient.api.BillingConfigResponseListener;
+import com.android.billingclient.api.GetBillingConfigParams;
 import com.android.billingclient.api.BillingClientStateListener;
 import com.android.billingclient.api.BillingFlowParams;
 import com.android.billingclient.api.BillingResult;
@@ -61,7 +63,8 @@ static final class MethodNames {
     static final String ACKNOWLEDGE_PURCHASE =
         "BillingClient#acknowledgePurchase(AcknowledgePurchaseParams, AcknowledgePurchaseResponseListener)";
     static final String IS_FEATURE_SUPPORTED = "BillingClient#isFeatureSupported(String)";
-    static final String GET_CONNECTION_STATE = "BillingClient#getConnectionState()";
+    static final String GET_CONNECTION_STATE = "BillingClient#getConnectionState()";;
+    static final String GET_BILLING_CONFIG = "BillingClient#getBillingConfig()";
 
     private MethodNames() {}
   }
@@ -184,11 +187,25 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result
       case MethodNames.GET_CONNECTION_STATE:
         getConnectionState(result);
         break;
+      case MethodNames.GET_BILLING_CONFIG:
+        getBillingConfig(result);
+        break;
       default:
         result.notImplemented();
     }
   }
 
+  private void getBillingConfig(final MethodChannel.Result result) {
+    billingClient.getBillingConfigAsync(
+        GetBillingConfigParams.newBuilder().build(),
+        (billingResult, billingConfig) -> {
+          final Map<String, Object> serialized = new HashMap<>();
+          serialized.put("billingResult", fromBillingResult(billingResult));
+          serialized.put("countryCode", billingConfig.getCountryCode());
+          result.success(serialized);
+        });
+  }
+
   private void endConnection(final MethodChannel.Result result) {
     endBillingClientConnection();
     result.success(null);