[billing] Restore QueryProductDetailsResult and QueryProductDetailsAsync() (#1207)

Fixes: #1206

This PR restores the QueryProductDetailsResult type and fixes the
QueryProductDetailsAsync behavior that was inadvertently broken in PR
#1200.

### Problem

In PR #1200, the billing client was updated from version 7.1.1 to
8.0.0, but the changes introduced a breaking change to the API:

The `QueryProductDetailsResult` class was removed the
`QueryProductDetailsAsync` method was changed to pass through a
`QueryProductDetailsResult` parameter directly instead of creating a new
instance This created an inconsistent state where the code referenced
a type that no longer existed.

### Solution

Updated the nugetVersion from 8.0.0 to 8.0.0.1 to reflect the latest
version of the NuGet package.

Enhancements to Product Details Handling:

* Restored the `QueryProductDetailsResult` class with properties for
  `BillingResult` and `ProductDetailsList`. Marked the
  `ProductDetails` property as obsolete to encourage the use of
  `ProductDetailsList`.

* Updated the `OnProductDetailsResponse` method in
  `InternalProductDetailsResponseListener` to initialize
  `QueryProductDetailsResult` if null and set the Result property
  before invoking the response handler.

Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>

Author: Copilot

config.json

@@ -2167,7 +2167,7 @@
         "groupId": "com.android.billingclient",
         "artifactId": "billing",
         "version": "8.0.0",
-        "nugetVersion": "8.0.0",
+        "nugetVersion": "8.0.0.1",
         "nugetId": "Xamarin.Android.Google.BillingClient",
         "type": "xbd"
       },

source/com.android.billingclient/billing/Additions/Additions.cs

@@ -27,6 +27,20 @@ public class QuerySkuDetailsResult
         public IList<SkuDetails> SkuDetails { get; set; }
     }
 
+    public partial class QueryProductDetailsResult
+    {
+        public QueryProductDetailsResult() { }
+
+        public BillingResult Result { get; set; }
+
+        [Obsolete ($"Use {nameof(ProductDetailsList)} instead")]
+        public IList<ProductDetails> ProductDetails
+        {
+            get => ProductDetailsList;
+            set { /* Obsolete property setter does nothing */ }
+        }
+    }
+
     public class QueryPurchasesResult
     {
         public BillingResult Result { get; set; }
@@ -241,7 +255,11 @@ internal class InternalProductDetailsResponseListener : Java.Lang.Object, IProdu
         public Action<BillingResult, QueryProductDetailsResult> ProductDetailsResponseHandler { get; set; }
 
         public void OnProductDetailsResponse(BillingResult result, QueryProductDetailsResult queryResult)
-            => ProductDetailsResponseHandler?.Invoke(result, queryResult);
+        {
+            queryResult ??= new();
+            queryResult.Result = result;
+            ProductDetailsResponseHandler?.Invoke(result, queryResult);
+        }
     }
 
     internal class InternalPurchasesResponseListener : Java.Lang.Object, IPurchasesResponseListener