Update components E2E test to use splatting (#11518)

This test was already in place, and just needs some updates to work with
Razor syntax instead of .cs

Author: rynowak

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

@@ -7,18 +7,12 @@
 
 <div id="duplicate-on-element-override">
     <DuplicateAttributesOnElementChildComponent
-        BoolAttributeBefore="true"
-        StringAttributeBefore="original-text"
         UnmatchedValues="@elementValues"
         BoolAttributeAfter="false"
         StringAttributeAfter="other-text" />
 </div>
 
 @functions {
-    void SomeMethod()
-    {
-    }
-
     Dictionary<string, object> elementValues = new Dictionary<string, object>()
     {
         { "bool",  true },

src/Components/test/testassets/BasicTestApp/DuplicateAttributesOnElementChildComponent.cs

@@ -0,0 +1,23 @@
+@if (StringAttributeBefore != null)
+{
+    <div string="@StringAttributeBefore"
+         bool="@BoolAttributeBefore"
+         @attributes="@UnmatchedValues">
+    </div>
+}
+else
+{
+    <div @attributes="@UnmatchedValues"
+         string="@StringAttributeAfter"
+         bool="@BoolAttributeAfter">
+    </div>
+}
+
+@code {
+    [Parameter] public string StringAttributeBefore { get; private set; }
+    [Parameter] public bool BoolAttributeBefore { get; private set; }
+    [Parameter] public string StringAttributeAfter { get; private set; }
+    [Parameter] public bool? BoolAttributeAfter { get; private set; }
+
+    [Parameter(CaptureUnmatchedValues = true)] public Dictionary<string, object> UnmatchedValues { get; private set; }
+}