Add additional validation for Virtualization test (#26904)

* Add additional validation for Virtualization test

* Update VirtualizationTest.cs

Author: captainsafia

src/Components/test/E2ETest/Tests/VirtualizationTest.cs

@@ -208,6 +208,10 @@ public void CanUseViewportAsContainer()
 
             Browser.ExecuteJavaScript("window.scrollTo(0, document.body.scrollHeight);");
 
+            // Validate that the scroll event completed successfully
+            var lastElement = Browser.Exists(By.Id("999"));
+            Browser.True(() => lastElement.Displayed);
+
             // Validate that the top spacer has expanded.
             Browser.NotEqual(expectedInitialSpacerStyle, () => topSpacer.GetAttribute("style"));
         }

src/Components/test/testassets/BasicTestApp/VirtualizationComponent.razor

@@ -31,7 +31,7 @@
 <p id="viewport-as-root">
     Viewport as root:<br />
     <Virtualize Items="@fixedItems" ItemSize="itemSize">
-        <div @key="context" style="height: @(itemSize)px; background-color: rgb(@((context % 2) * 255), @((1-(context % 2)) * 255), 255);">Item @context</div>
+        <div @key="context" id="@context" style="height: @(itemSize)px; background-color: rgb(@((context % 2) * 255), @((1-(context % 2)) * 255), 255);">Item @context</div>
     </Virtualize>
 </p>